Date: Thu, 10 Jun 1999 22:30:25 -0500 From: Simple Nomad To: BUGTRAQ@netspace.org Subject: Info on Worm.ExploreZip Info on Worm.ExploreZip: I'm in the process of cleanup - my day job employer got hit, and we're NT with no 95/98 to speak of. Here are some interesting tidbits that I haven't seen on some of the commercial Anti-Virus web sites regarding NT. Payload: - The trojan can come into any email client, obviously. If executed, it will proceed to go active in memory. In other words, you do not need Outlook for the Payload to activate, just a Win32 machine. A Notes mail client user probably did the most damage in our environment to network NT file servers. - It will have a process running called _setup.exe, zipped_f.exe, and possibly explore.exe. - One of our users reported seeing explore.exe running as an application, although I wasn't able to confirm this. - It deletes files with *.h, *.c, *.cpp, *.asm, *.doc, *.xls, and *.ppt extensions on all drives (C through Z) that are currently mapped. - Every few minutes it will repeat the deletion process. This is particularly nasty if you are trying to do restores to network drives while the virus is still active in your environment. Progation: - On the Melissa-style method of propagation, it checks the user's Inbox in Outlook. The Outlook client does not have to be running, as the trojan uses MAPI calls. - Propagation is triggered by the arrival of a new message into the Outlook's Inbox. - Once triggered, the virus takes the first two names in the header and uses it to plug into the text of the message. If more than one user name is in the message header (possible if you are using distribution lists or role-based mail boxes that forward mail to multiple people) it is possible the names will not be in the correct order. Also if you use Lastname, Firstname as a naming convention you will get Lastname, plugged into the messages. - It creates the message with the names and attaches the trojan, naming it zipped_files.exe with the happy message as reported on most Anti-Virus vendor sites. - In other words, you send an email to billg@microsoft.com with a subject of Microsoft Sucks, he's infected and his machine is up and running, you will get a reply with a subject of Re: Microsoft Sucks with the attachment. I mean he says he'll get back with you and to read the attached zipped docs, and you being Joe/Josey corporate user check it out. False message saying it's a corrupt zip, blah, blah, blah, and now you're sending out trojans. We got hit when email was sent to some engineers at Microsoft, and the reply came back with the trojan. The nature of the email sent to Microsoft was "where is the info we requested" so it seemed natural that the attachment was supposed to be a self-extracting zip. That's right, Microsoft got hit, so I would guess a few source code files and Office docs were wiped. Hopefully as Microsoft starts the slow process of restoring Office docs and source code (!) they will discover what the rest of us have known all along -- the security model is less than ideal (which is, um, an understatement). Another interesting note, the APIs that the Exchange Anti-Virus vendors use to scan Exchange mailstores only scan on messages inbound to the mailstore. This means that outbound messages are not scanned. We had an affected machine that replied to messages from the Internet with the trojan attachment as our Exchange outbound goes straight to a Unix machine on its way to the Internet. Fortunately we had a process running on the Unix box to catch inbound and outbound email with the attachments named zipped_files.exe and it was stopped, but this was why we saw our Exchange AntiVirus *not* catch the message. Why do the Anti-Virus vendors only use APIs that catch inbound messages? Because that is all Microsoft has given them. Most of the vendors have really been pressuring Microsoft to release info about coding to check for outbound messages. Final tidbits (sorry if this message isn't very coherent, it's late and I've been up a long time): the trojan was written using Borland Delphi, and was possibly compiled on April 14, 1999. Obviously the virus writer got the idea for the propagation method from Melissa, and one can only wonder what the next worm/trojan/virus will do. Simple Nomad // thegnome@nmrc.org // ....no rest for the Wicca'd.... www.nmrc.org // ---------------------------------------------------------------------------- Date: Thu, 10 Jun 1999 23:58:21 -0400 From: CERT Advisory Reply-To: cert-advisory-request@cert.org To: cert-advisory@coal.cert.org Subject: CERT Advisory CA-99.06 - ExploreZip Trojan Horse Program -----BEGIN PGP SIGNED MESSAGE----- CERT Advisory CA-99-06 ExploreZip Trojan Horse Program Original issue date: Thursday June 10, 1999 Source: CERT/CC Systems Affected * Machines running Windows 95, Windows 98, or Windows NT. * Any mail handling system could experience performance problems or a denial of service as a result of the propagation of this Trojan horse program. Overview The CERT Coordination Center continues to receive reports and inquiries regarding various forms of malicious executable files that are propagated as file attachments in electronic mail. Most recently, the CERT/CC has received reports of sites affected by ExploreZip, a Windows Trojan horse program. I. Description The CERT/CC has received reports of a Trojan horse program that is propagating in email attachments. This program is called ExploreZip. The number and variety of reports we have received indicate that this has the potential to be a widespread attack affecting a variety of sites. Our analysis indicates that this Trojan horse program requires the victim to run the attached zipped_files.exe program in order install a copy of itself and enable propagation. Based on reports we have received, systems running Windows 95, Windows 98, and Windows NT are the target platforms for this Trojan horse program. It is possible that under some mailer configurations, a user might automatically open a malicious file received in the form of an email attachment. This program is not known to exploit any new vulnerabilities. While the primary transport mechanism of this program is via email, any way of transferring files can also propagate the program. The ExploreZip Trojan horse has been propagated in the form of email messages containing the file zipped_files.exe as an attachment. The body of the email message usually appears to come from a known email correspondent, and may contain the following text: I received your email and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs. The subject line of the message may not be predictable and may appear to be sent in reply to previous email. Opening the zipped_files.exe file causes the program to execute. At this time, there is conflicting information about the exact actions taken by zipped_files.exe when executed. One possible reason for conflicting information may be that there are multiple variations of the program being propagated, although we have not confirmed this one way or the other. Currently, we have the following general information on actions taken by the program. * The program searches local and networked drives (drive letters C through Z) for specific file types and attempts to erase the contents of the files, leaving a zero byte file. The targets may include Microsoft Office files, such as .doc, .xls, and .ppt, and various source code files, such as .c, .cpp, .h, and .asm. * The program propagates by replying to any new email that is received by an infected computer. A copy of zipped_files.exe is attached to the reply message. * The program creates an entry in the Windows 95/98 WIN.INI file: run=C:\WINDOWS\SYSTEM\Explore.exe On Windows NT systems, an entry is made in the system registry: [HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows] run = "c:\winnt\system32\explore.exe" * The program creates a file called explore.exe in the following locations: Windows 95/98 - c:\windows\system\explore.exe Windows NT - c:\winnt\system32\explore.exe This file is a copy of the zipped_files.exe Trojan horse, and the file size is 210432 bytes. MD5 (Explore.exe) = 0e10993050e5ed199e90f7372259e44b We will update this advisory with more specific information as we are able to confirm details. Please check the CERT/CC web site for the current version containing a complete revision history. II. Impact * Users who execute the zipped_files.exe Trojan horse will infect the host system, potentially causing targeted files to be destroyed. * Indirectly, this Trojan horse could cause a denial of service on mail servers. Several large sites have reported performance problems with their mail servers as a result of the propagation of this Trojan horse. III. Solution Use virus scanners In order to detect and clean current viruses you must keep your scanning tools up to date with the latest definition files. Please see the following anti-virus vendor resources for more information about the characteristics and removal techniques for the malicious file known as ExploreZip. Central Command http://www.avp.com/upgrade/upgrade.html Command Software Systems, Inc http://www.commandcom.com/html/virus/explorezip.html Computer Associates http://support.cai.com/Download/virussig.html Data Fellows http://www.datafellows.com/news/pr/eng/19990610.htm McAfee, Inc. (a Network Associates company) http://www.mcafee.com/viruses/explorezip/protecting_yourself.as p Network Associates Incorporated http://www.avertlabs.com/public/datafiles/valerts/vinfo/va10185 .asp Sophos, Incorporated http://www.sophos.com/downloads/ide/index.html#explorez Symantec http://www.sarc.com/avcenter/download.html Trend Micro Incorporated http://www.antivirus.com/download/pattern.htm General protection from email Trojan horses and viruses Some previous examples of malicious files known to have propagated through electronic mail include * False upgrade to Internet Explorer - discussed in CA-99-02 http://www.cert.org/advisories/CA-99-02-Trojan-Horses.html * Melissa macro virus - discussed in CA-99-04 http://www.cert.org/advisories/CA-99-04-Melissa-Macro-Virus.html * Happy99.exe Trojan Horse - discussed in IN-99-02 http://www.cert.org/incident_notes/IN-99-02.html * CIH/Chernobyl virus - discussed in IN-99-03 http://www.cert.org/incident_notes/IN-99-03.html In each of the above cases, the effects of the malicious file are activated only when the file in question is executed. Social engineering is typically employed to trick a recipient into executing the malicious file. Some of the social engineering techniques we have seen used include * Making false claims that a file attachment contains a software patch or update * Implying or using entertaining content to entice a user into executing a malicious file * Using email delivery techniques which cause the message to appear to have come from a familiar or trusted source * Packaging malicious files in deceptively familiar ways (e.g., use of familiar but deceptive program icons or file names) The best advice with regard to malicious files is to avoid executing them in the first place. CERT advisory CA-99-02 discusses Trojan horses and offers suggestions to avoid them (please see Section V). http://www.cert.org/advisories/CA-99-02-Trojan-Horses.html Additional information Additional sources of virus information are listed at http://www.cert.org/other_sources/viruses.html ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-99-06-explorezip.html. ______________________________________________________________________ CERT/CC Contact Information Email: cert@cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryption We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key. If you prefer to use DES, please call the CERT hotline for more information. Getting security information CERT publications and other security information are available from our web site http://www.cert.org/. To be added to our mailing list for advisories and bulletins, send email to cert-advisory-request@cert.org and include SUBSCRIBE your-email-address in the subject of your message. Copyright 1999 Carnegie Mellon University. Conditions for use, disclaimers, and sponsorship information can be found in http://www.cert.org/legal_stuff.html. * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. Revision History June 10, 1999: Initial release -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBN2B33nVP+x0t4w7BAQEsGQQAjO8XmCFoS5bE4l3+fDdrd7vUGHn3l1WZ HyUPO25ddtd50rsyHCTaSuxr9HUuzswm4DI+T80y6nt5i+NTiSIKWjL0Qo8C+9Xn BsHQqjmRdDrWD/r6+ZHnoekrgNWWM+1Uy8XITOyzfntGA2mGz/DGkyHq4afElZw6 3SLhZ6GPtjA= =Ja0e -----END PGP SIGNATURE----- ---------------------------------------------------------------------------- Date: Fri, 11 Jun 1999 15:38:50 +1000 From: Brad Griffin To: BUGTRAQ@netspace.org Subject: (Fwd) AVP News for 06/10/1999 - VIRUS ALERT This was posted by the AVP people (you've all probably seen it) ------- Forwarded Message Follows ------- >From: "News Manager" Organization: Central Command Inc. To: avp-news@avp.com Date sent: Thu, 10 Jun 1999 15:58:28 -0400 Subject: AVP News for 06/10/1999 - VIRUS ALERT Send reply to: newsmgr@avp.com AntiViral Toolkit Pro Newsletter for 06/10/1999 =============================================== If you suspect a virus infection you can download a free time limted, fully functional trial version of AntiViral Toolkit Pro from http://www.avp.com VIRUS ALERT - I-Worm.ZippedFiles AntiViral Toolkit Pro has been updated to detect and remove this virus. I-Worm.ZippedFiles This is a worm virus spreading via Internet. It appears as a "Zipped_Files.Exe" file attached to email. This file itself is a Delphi executable files about 210Kb of length. The most part of file's code is occupied by Delphi run-time libraries, data and classes, and just about 10Kb of code is "pure" worm code. Being executed it installs itself into the system, then sends infected messages (with its attached copy) to addresses using addresses found in emails in the Inbox. To hide its activity the worm displays the message: To install into the system the virus copies itself to Windows directory with the _SETUP.EXE name and to Windows system directory with EXPLORE.EXE name, for example: C:\WINDOWS\_SETUP.EXE C:\WINDOWS\SYSTEM\EXPLORE.EXE The worm then registers its copy in the Windows configuration file WIN.INI to force the system to execute it each time Windows starts up. To do that the worm writes the instruction "run=" to the [windows] section there. Depending on the worm "status" and system conditions there are two possible variants of this instruction, for example: run=_setup.exe run=C:\WINDOWS\SYSTEM\Explore.exe The worm then stays "memory resident" and is active up to the moment the system shuts down. The worm's task has no active window and is not visible in taskbar, but is visible in the task list (Ctrl-Alt- Del) with one of the names the worm use to name their copies: Zipped_files Explore _setup The worm does not check its copy already presented in the Windows memory, and as a result there may be several worm's instances found. Being active as a Windows application the worm runs four threads of its main process: installation thread that copies worm files to the Windows directories and registers them, the Internet spreading thread and two files destroying threads. The second (most important) thread sends the email messages using any email system based on standard MAPI (Messaging Application Program Interface) - MS Outlook, MS Outlook Express, e.t.c. The worm knocks to the installed E-mail system four times trying to logon with different MAPI profiles: default one, Microsoft Outlook, Microsoft Outlook Internet Settings, Microsoft Exchange. Being connected to the E-mail the worm monitors all arriving messages - in endless loop it scans Inbox for messages and reply to them. The reply message has the same Subject with "Re" prefix, the body of message looks like follows: Hi [recipient name] I received your email and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs. The message ends with one of two variants of signature: bye. sincerely [sender name] The copy of worm is attached to the message with the "Zipped_Files.Exe" name. The worm does not reply on the messages twice and does not reply its own messages. To detect already affected messages the worm marks them with TAB character at the end of Subject string. Each time the worm scans Inbox for messages, it gets Subject field, goes to its end, and skips the message if TAB is found there. The worm also does not reply all messages in Inbox but unread messages only. It is necessary to note that both these conditions (reply unread messages only and do not reply the same message twice) are optional in the worm's infection routine. In known worm version both of them are hardcoded the way described above, but it is possible that the next worm version will answer all messages in Inbox each time the worm infection thread gets control. As a result the things look like follows. When the worm starts for the first time on the computer, it sends infected messages by using all unread messages found in the Inbox. It marks them as "affected" by TAB character and does not affect anymore. When a new message is received from the Internet and appears in the Inbox, it is immediately "answered" by worm with the fake text shown above. The virus has extremely dangerous payload. Each time it is executed, it runs two more threads that scan directory trees on the local and network drives, look for .C, .H, .CPP, .ASM, .DOC, .XLS, .PPT (programs' source and MS Office files) and zeroes them. The worm uses a create-and-close trick that erases file contents and sets file length to zero. As a result the files become unrecoverable. As it is mentioned above, there are two files killing threads. First of them is active all time the worm copy is active in the system - till the shutting down. In endless loop it scans all available drives from C: to Z: and corrupts files that were listed above. The second thread is executed only once. It enumerates network resources, scans them for the same files and also destroys them. ------------------------------------------------------ You are receiving this newsletter because you subscribed to our free newsletter service. Central Command respects your online time and privacy. If you would refer not to receive future issues of the this newsletter you can unsubscribe yourself by sending a e-mail message to: majordomo@avp.com In the body of the message please include the following text to remove yourself from the mailing list: unsubscribe avp-news ------------------------------------------------------- - ========================================================= Central Command Inc. AntiViral Toolkit Pro Antivirus Specialists http://www.avp.com Complete Internet Virus Protection Visit the Virus Encyclopedia http://www.avpve.com ========================================================= Brad Griffin 2nd year BiT Central Queensland University Rockhampton QLD Australia ********************************** Is there anybody out there? Join 'Team Hypersurf' in the search for extra terrestrial intelligence. http://setiathome.ssl.berkeley.edu ********************************** ---------------------------------------------------------------------------- Date: Fri, 11 Jun 1999 18:25:24 -0700 (PDT) From: CIAC Mail User To: ciac-bulletin@rumpole.llnl.gov Subject: CIAC Bulletin J-047: The ExploreZip Worm [ For Public Release ] -----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN The ExploreZip Worm June 11, 1999 23:00 GMT Number J-047 ______________________________________________________________________________ PROBLEM: A new worm program named zipped_files.exe spreads itself as an attachment to e-mail messages and destroys document files. PLATFORM: Windows 95, Windows 98, and Windows NT. Outlook or Exchange are need to spread. DAMAGE: The worm sends copies of itself to everyone in your inbox and destroys files with the extensions: .h, .c, .cpp, .asm, .doc, .xls, and .ppt. SOLUTION: Do not automatically run an attached file named zipped_files.exe even if it appears to have come from a friend. Update your antivirus software to detect this worm. ______________________________________________________________________________ VULNERABILITY Severe Risk: While this worm does not appear to be spreading ASSESSMENT: as rapidly as the Melissa virus, the payload can do severe damage to an organization by deleting all Microsoft Office documents and computer program source files. ______________________________________________________________________________ The ExploreZip Worm Introduction ============ CIAC has received reports of the spread of a new worm program called ExploreZip (alias: W32/ExploreZip.worm, Worm.ExploreZip). The worm spreads in a manner similar to the W97M.Melissa virus. The worm arrives as an attachment to an e- mail message. When a user double clicks on that attachment, the worm program runs and spreads itself by sending replies to all the mail in your inbox with the worm program as an attachment. Different from the Melissa macro virus, this is a worm program in that it does not infect other programs or documents. It is also executable code instead of a macro program so the macro detection capability in Microsoft Word will not protect you from this worm. The worm has a payload that destroys Microsoft Office documents and program source code files. As this is object code (binary) it only runs on INTEL platforms running Windows 95, Windows 98, and Windows NT. It cannot run on Macintosh or other hardware types and cannot run on earlier versions of windows or on DOS. In order to spread using e-mail, the worm needs Outlook or Microsoft Exchange. However, the payload will run and destroy files even if the program cannot spread itself via e-mail. Worm Operation ============== The worm is an executable program named "Zipped_files.exe" that appears to be a self extracting ZIP archive. It arrives as an attachment to an e-mail message with the following content: Hi ! I received your email and I shall send you a reply ASAP. Til then, take a look at the attached zipped docs. bye The message appears to be a reply to one of your messages. The subject of the mail message is variable and appears to be a reply to a message from you. When a user double clicks on the attached worm program, it puts up the following dialog box that makes the file appear to be a damaged zip archive. .------------------------------------------------------------------. | Error X| |------------------------------------------------------------------| | | | X Cannot open file: it does not appear to be a valid archive.| | If this file is part of a ZIP format backup set, insert | | the last disk of the backup set and try again. Please | | press F1 for help. | | ------------- | | | OK | | | ------------- | - -------------------------------------------------------------------- Pressing F1 does nothing and clicking OK simply closes the dialog box. If WinZip is installed on the system, it will open with the empty zip file: Zipped_files.zip, again making it appear to be a damaged zip archive. As the worm continues executing, it searches the inbox of your mail program and sends a reply to every message it finds there, adding the message listed above and attaching the worm program file. When it has finished sending mail, it stores a copy of itself on your system and sets that copy to be executed at system startup time. On Windows 95 and Windows 98 systems, it stores a copy of itself in: c:\windows\system\explore.exe and places the following line in the win.ini file to restart the worm every time you run Windows. run=C:\WINDOWS\System\Explore.exe If your active windows directory is not C:\WINDOWS, replace C:\WINDOWS in the command and file location above with the path to your active Windows directory. On Windows NT systems, it stores copies of itself in: c:\winnt\system32\explore.exe c:\winnt\_setup.exe If your active Windows NT directory is not c:\winnt, replace c:\winnt in the file locations above with the path to your active Windows NT directory. The worm then changes the value of the following registry key to "_setup.exe", which runs the _setup.exe program at startup. HKEY_CURRENT_USER\Software\Microsoft\WindowsNT\ CurrentVersion\Windows\run After installing itself, the worm runs its payload. The payload searches your lettered hard disk drives (C: through Z:) for programming source code files with the extensions: .h .c .cpp .asm (C header files, C programs, C++ programs, and assembly language programs) and Microsoft Office documents with the extensions: .doc .xls .ppt (Word documents, Excel documents, and PowerPoint documents) and changes them to a zero length file, making them nearly impossible to recover. You might be able to recover parts of a file using a disk editor but that would be a difficult and time consuming process. Detecting An Infection ====================== Infections with ExploreZip are easy to detect. Press Ctrl-Alt-Del and open the Task Manager as shown here. On Windows NT, press Ctrl-Alt-Del, click the Task Manager button, and then choose the Processes tab. The dialog box shown by Windows NT is slightly different from that shown here but has the same function. .-----------------------------------------------------------. | Close Program ? X| |-----------------------------------------------------------| | -----------------------------------------------------| | | |Exploring-temp | | | |Explorer | | | |Zipped_file | | | |Osa | | | |Systray | | | |Navapw32 | | | |Winzip32 | | | | | | | | | | | -----------------------------------------------------| | | WARNING: Pressing CTRL-ALT-DEL again will restart your | | computer. You will lose unsaved information in all | | programs that are running. | | | | -------------- --------------- ------------ | | | End Task | | Shut Down | | Cancel | | | -------------- --------------- ------------ | - ------------------------------------------------------------- Note the task named Zipped_file (Zipped_files.ex on Windows NT). This is the running worm program. To stop it, select Zipped_file (or Zipped_files.ex) and click End Task. If you have restarted your system since the infection, you will see the process Explore (_setup.exe on Windows NT) instead of Zipped_file. Again, to stop that process, select it and click End Task. Do not confuse the task Explore with the task Explorer as they are different. The Explorer task is the Windows explorer program. Removing An Infection ===================== The easiest way to eliminate the worm from your system is to use an updated antivirus package. However, to do it by hand, perform these steps: 1. Press Ctrl-Alt-Del to open the task manager. 2. Select the Zipped_file or Explore (Zipped_files.ex or _setup.exe for Windows NT) process (whichever is running) and click End Task 3. Delete all copies of zipped_file.exe from your system. These will be in the download or attachments directory of your mail program. 4. Delete the file c:\windows\system\explore.exe or for Windows NT, delete c:\winnt\system32\explore.exe and c:\winnt\_setup.exe. 5. Edit c:\windows\win.ini and remove the line run=c:\windows\system\explore.exe Or in Windows NT, run Regedit.exe and delete the value of the key: HKEY_CURRENT_USER\Software\Microsoft\WindowsNT\ CurrentVersion\Windows\run Protection ========== Most antivirus vendors already have detection and removal capabilities available for this worm and we expect the others to have them soon. Of the vendors that have a solution available, you may need to download it from their web pages and not depend on the automatic update features of the product. We expect the automatic update features to have this worm definition soon. The following vendors have solutions now: Symantec (NAV) http://www.symantec.com/avcenter/venc/data/worm.explore.zip.html Network Associates (McAfee) http://vil.mcafee.com/vil/vpe10183.asp DataFellows (F-PROT) http://www.datafellows.com/v-descs/zipped.htm Trend http://www.antivirus.com/vinfo/alerts.htm All users are cautioned to think before double clicking on a file included as an attachment to any e-mail message, even if that message appears to come from a friend. If that attachment is a Microsoft Office document and you have macro detection turned on, then you can double click the attachment and the macro detection capability will stop the document from loading if it contains a macro program. It will then give you the choice to enable or disable the macros. Remember, disable macros unless you are expecting to receive them. If the attachment is an executable program, scan it with your antivirus utility before running it. If it passes the antivirus scan, you might still want to reconsider running it if it comes from someone you do not know or is an unexpected delivery from someone you do know. Call the person up on the phone (don't send them e-mail) and ask him if he sent you an executable before running the file. If you send him an e-mail and he is infected with this worm, you will likely receive a reply (from the worm) saying "take a look at the attached zipped docs". If the file is a self extracting archive, open it with the archive program (for example, WinZip) instead of running the archive itself. You can still get the files out of the archive but without running the executable part (the self extractor) of the archive file. ______________________________________________________________________________ Thanks to Symantec and Network Associates for their early warning and analysis of this worm. ______________________________________________________________________________ For additional information or assistance, please contact CIAC: CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), use one of the following methods to contact CIAC: 1. Call the CIAC voice number 925-422-8193 and leave a message, or 2. Call 888-449-8369 to send a Sky Page to the CIAC duty person or 3. Send e-mail to 4498369@skytel.com, or 4. Call 800-201-9288 for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov) Modem access: +1 (925) 423-4753 (28.8K baud) +1 (925) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 3. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called Majordomo, which ignores E-mail header subject lines. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-mail message body, substituting ciac-bulletin, spi-announce OR spi-notes for list-name: E-mail to ciac-listproc@llnl.gov or majordomo@rumpole.llnl.gov: subscribe list-name e.g., subscribe ciac-bulletin You will receive an acknowledgment email immediately with a confirmation that you will need to mail back to the addresses above, as per the instructions in the email. This is a partial protection to make sure you are really the one who asked to be signed up for the list in question. If you include the word 'help' in the body of an email to the above address, it will also send back an information file on how to subscribe/unsubscribe, get past issues of CIAC bulletins via email, etc. PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) J-036: LDAP Buffer overflow against Microsoft Directory Services J-037: W97M.Melissa Word Macro Virus J-038: HP-UX Vulnerabilities (hpterm, ftp) J-039: HP-UX Vulnerabilities (MC/ServiceGuard & MC/LockManager, DES J-040: HP-UX Security Vulnerability in sendmail J-041: Cisco IOS(R) Software Input Access List Leakage with NAT J-042: Web Security J-043: (bulletin in process) J-044: Tru64/Digital UNIX (dtlogin) Security Vulnerability J-045: Vulnerability in statd exposes vulnerability in automountd J-046: HP-UX VVOS NES Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBN2G1vLnzJzdsy3QZAQFjjgQA7vSRm+LAIrtr1Q7PgLaePYfe3Ezjm0La A3B7PbRZMBTXe7e36oz0bBWXrQyP6aDDZosdHRsF3vUb04azUXvgh1fLgTFKACZm ePBuhrYLMehXmyqoOg657RspMGUBgPrxp9czgT5OGjnlkJtfcQmqkxG5vAfLJCO1 SRYPusNb4sw= =E5Pv -----END PGP SIGNATURE----- ---------------------------------------------------------------------------- Date: Mon, 14 Jun 1999 07:21:34 -0400 From: CERT Advisory Reply-To: cert-advisory-request@cert.org To: cert-advisory@coal.cert.org Subject: CERT Advisory CA-99.06 - New information regarding ExploreZip -----BEGIN PGP SIGNED MESSAGE----- CERT Advisory CA-99-06-explorezip Original issue date: Thursday June 10, 1999 Last Revised Date: June 14, 1999 Added information about the program's self-propagation via networked shares; also updated anti-virus vendor URLs. Source: CERT/CC Note: The CERT Coordination Center has discovered new information regarding the ExploreZip worm. This re-issue of CERT Advisory CA-99-06 contains new information regarding an additional means by which the Worm can spread, and a caution about disinfecting your systems. We will continue to update this advisory as new information is discovered. We encourage you to check our web site frequently for any new information. Systems Affected * Machines running Windows 95, Windows 98, or Windows NT. * Machines with filesystems and/or shares that are writable by a user of an infected system. * Any mail handling system could experience performance problems or a denial of service as a result of the propagation of this Trojan horse program. Overview The CERT Coordination Center continues to receive reports and inquiries regarding various forms of malicious executable files that are propagated as file attachments in electronic mail. During the second week of June 1999, the CERT/CC began receiving reports of sites affected by ExploreZip, a Trojan horse/worm program that affects Windows systems and has propagated in email attachments. The number and variety of reports we have received indicate that this has the potential to be a widespread attack affecting a variety of sites. I. Description Our original analysis indicated that the ExploreZip program is a Trojan horse, since it initially requires a victim to open or run an email attachment in order for the program to install a copy of itself and enable further propagation. Further analysis has shown that, once installed, the program may also behave as a worm, and it may be able to propagate itself, without any human interaction, to other networked machines that have certain writable shares. The ExploreZip Trojan horse has been propagated between users in the form of email messages containing an attached file named zipped_files.exe. Some email programs may display this attachment with a "WinZip" icon. The body of the email message usually appears to come from a known email correspondent, and typically contains the following text: I received your email and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs. The subject line of the message may not be predictable and may appear to be sent in reply to previous email. Opening the zipped_files.exe file causes the program to execute. It is possible under some mailer configurations that a user might automatically open a malicious file received in the form of an email attachment. When the program is run, an error message is displayed: Cannot open file: it does not appear to be a valid archive. If this file is part of a ZIP format backup set, insert the last disk of the backup set and try again. Please press F1 for help. Destruction of files * The program searches local and networked drives (drive letters C through Z) for specific file types and attempts to erase the contents of the files, leaving a zero byte file. The targets may include Microsoft Office files, such as .doc, .xls, and .ppt, and various source code files, such as .c, .cpp, .h, and .asm. * The program may also be able to delete files that are writable to it via SMB/CIFS file sharing. The program appears to look through the network neighborhood and delete any files that are shared and writable, even if those shares are not mapped to networked drives on the infected computer. * The program appears to continually delete the contents of targeted files on any mapped networked drives. The program does not appear to delete files with the "hidden" or "system" attribute, regardless of their extension. System modifications * The zipped_files.exe program creates a copy of itself in a file called explore.exe in the following location(s): On Windows 98 - C:\WINDOWS\SYSTEM\Explore.exe On Windows NT - C:\WINNT\System32\Explore.exe This explore.exe file is an identical copy of the zipped_files.exe Trojan horse, and the file size is 210432 bytes. MD5 (Explore.exe) = 0e10993050e5ed199e90f7372259e44b * On Windows 98 systems, the zipped_files.exe program creates an entry in the WIN.INI file: run=C:\WINDOWS\SYSTEM\Explore.exe On Windows NT systems, an entry is made in the system registry: [HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows] run = "C:\WINNT\System32\Explore.exe" Propagation via file sharing Once explore.exe is running, it takes the following steps to propagate to other systems via file sharing: * Each time the program is executed, the program will search the network for all shares that contain a WIN.INI file with a valid "[windows]" section in the file. * For each such share that it finds, the program will attempt to + copy itself to a file named _setup.exe on that share + modify the WIN.INI file on that share by adding the entry "run=_setup.exe" The account running the program on the original infected machine needs to have permission to write to the second victim's shared directory. (That is, no vulnerabilities are being exploited in order for the program to spread in this manner.) The _setup.exe file is identical to the zipped_files.exe and explore.exe files on the original infected machine. * The original infected system will continue to scan shares that have been mapped to a local drive letter containing a valid WIN.INI file. For each such share that is found, the program will "re-infect" the victim system as described above. On Windows 98 systems that have a "run=_setup.exe" entry in the WIN.INI file (as described previously), the C:\WINDOWS\_setup.exe program is executed automatically whenever a user logs in. On Windows NT systems, a "run=_setup.exe" entry in the WIN.INI file does not appear to cause the program to be executed automatically. When run as _setup.exe, the program will attempt to * make another copy of itself in C:\WINDOWS\SYSTEM\Explore.exe * modify the WIN.INI file again by replacing the "run=_setup.exe" entry with "run=C:\WINDOWS\SYSTEM\Explore.exe" Note that when the program is run as _setup.exe, it configures the system to later run as explore.exe. But when run as explore.exe, it attempts to infect shares with valid WIN.INI files by configuring those files to run _setup.exe. Since this infection process includes local shares, affected systems may exhibit a "ping pong" behavior in which the infected host alternates between the two states. Propagation via email The program propagates by replying to any new email that is received by the infected computer. The reply messages are similar to the original email described above, each containing another copy of the zipped_files.exe attachment. We will continue to update this advisory with more specific information as we are able to confirm details. Please check the CERT/CC web site for the current version containing a complete revision history. II. Impact * Users who execute the zipped_files.exe Trojan horse will infect the host system, potentially causing targeted files to be destroyed. * Users who execute the Trojan horse may also infect other networked systems that have writable shares. * Because of the large amount of network traffic generated by infected machines, network performance may suffer. * Indirectly, this Trojan horse could cause a denial of service on mail servers. Several large sites have reported performance problems with their mail servers as a result of the propagation of this Trojan horse. III. Solution Use virus scanners While many anti-virus products are able to detect and remove the executables locally, because of the continuous re-infection process, simply removing all copies of the program from an infected system may leave your system open to re-infection at a later time, perhaps immediately. To prevent re-infection, you must not serve any shares containing a WIN.INI file to any potentially infected machines. If you share files with everyone in your domain, then you must disable shares with WIN.INI files until every machine on your network has been disinfected. In order to detect and clean current viruses, you must keep your scanning tools up to date with the latest definition files. Please see the following anti-virus vendor resources for more information about the characteristics and removal techniques for the malicious file known as ExploreZip. Aladdin Knowledge Systems, Inc. http://www.esafe.com/vcenter/explore.html Central Command http://www.avp.com/zippedfiles/zippedfiles.html Command Software Systems, Inc http://www.commandcom.com/html/virus/explorezip.html Computer Associates http://www.cai.com/virusinfo/virusalert.htm Data Fellows http://www.datafellows.com/news/pr/eng/19990610.htm McAfee, Inc. (a Network Associates company) http://www.mcafee.com/viruses/explorezip/default.asp Network Associates Incorporated http://www.avertlabs.com/public/datafiles/valerts/vinfo/va10185 .asp Sophos, Incorporated http://www.sophos.com/downloads/ide/index.html#explorez Symantec http://www.symantec.com/avcenter/venc/data/worm.explore.zip.htm l Trend Micro Incorporated http://www.antivirus.com/vinfo/alerts.htm Additional sources of virus information are listed at http://www.cert.org/other_sources/viruses.html Additional suggestions * Blocking Netbios traffic at your network border may help prevent propagation via shares from outside your network perimeter. * Disable file serving on workstations. You will not be able to share your files with other computers, but you will be able to browse and get files from servers. This will prevent your workstation from being infected via file sharing propagation. * Maintain a regular, off-line, backup cycle. General protection from email Trojan horses and viruses Some previous examples of malicious files known to have propagated through electronic mail include * False upgrade to Internet Explorer - discussed in CA-99-02 http://www.cert.org/advisories/CA-99-02-Trojan-Horses.html * Melissa macro virus - discussed in CA-99-04 http://www.cert.org/advisories/CA-99-04-Melissa-Macro-Virus.html * Happy99.exe Trojan Horse - discussed in IN-99-02 http://www.cert.org/incident_notes/IN-99-02.html * CIH/Chernobyl virus - discussed in IN-99-03 http://www.cert.org/incident_notes/IN-99-03.html In each of the above cases, the effects of the malicious file are activated only when the file in question is executed. Social engineering is typically employed to trick a recipient into executing the malicious file. Some of the social engineering techniques we have seen used include * Making false claims that a file attachment contains a software patch or update * Implying or using entertaining content to entice a user into executing a malicious file * Using email delivery techniques which cause the message to appear to have come from a familiar or trusted source * Packaging malicious files in deceptively familiar ways (e.g., use of familiar but deceptive program icons or file names) The best advice with regard to malicious files is to avoid executing them in the first place. CERT advisory CA-99-02 discusses Trojan horses and offers suggestions to avoid them (please see Section V). http://www.cert.org/advisories/CA-99-02-Trojan-Horses.html ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-99-06-explorezip.html. ______________________________________________________________________ CERT/CC Contact Information Email: cert@cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryption We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key. If you prefer to use DES, please call the CERT hotline for more information. Getting security information CERT publications and other security information are available from our web site http://www.cert.org/. To be added to our mailing list for advisories and bulletins, send email to cert-advisory-request@cert.org and include SUBSCRIBE your-email-address in the subject of your message. Copyright 1999 Carnegie Mellon University. Conditions for use, disclaimers, and sponsorship information can be found in http://www.cert.org/legal_stuff.html. * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. Revision History June 10, 1999: Initial release June 11, 1999: Added information about the appearance of the attached file Added information from Aladdin Knowledge Systems, Inc. June 14, 1999: Added information about the program's self-propagation via networked shares; also updated anti-virus vendor URLs -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBN2TZfHVP+x0t4w7BAQF7HAP/c7MLHxFQ2M9XXK5qweZISimvGdsdr6cn rd+S+QKsVPxKX64LikccAW8pu7d38nqNcMUhWDCge0k4eZmKWrN5uh4/znCV8ETE 2pttxe4t0Slo8B9r2Es5LafIWInfZGuDRHRYIuWyrPe9ReEtUrKx52/1DSu7ZTO9 esjkyG7T22o= =+n1t -----END PGP SIGNATURE-----