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                                @stake, Inc.
                              www.atstake.com

                             Security Advisory

Advisory Name: AppleFileServer Remote Command Execution
 Release Date: 05/03/2004
  Application: AppleFileServer
     Platform: MacOS X 10.3.3 and below
     Severity: A remote attacker can execute arbitrary
               commands as root
      Authors: Dave G. <daveg@atstake.com>
               Dino Dai Zovi <ddaizovi@atstake.com>
Vendor Status: Informed, Upgrade Available
CVE Candidate: CAN-2004-0430
    Reference: www.atstake.com/research/advisories/2004/a050304-1.txt


Overview:

The AppleFileServer provides Apple Filing Protocol (AFP) services for
both Mac OS X and Mac OS X server.  AFP is a protocol used to
remotely mount drives, similar to NFS or SMB/CIFS.  There is a
pre-authentication, remotely exploitable stack buffer overflow that
allows an attacker to obtain administrative privileges and execute
commands as root. 


Details:

The AppleFileServer provides Apple Filing Protocol (AFP) services
for both Mac OS X and Mac OS X server.  AFP is a protocol used to
remotely mount drives, similar to NFS or SMB/CIFS.  AFP is not
enabled by default. It is enabled through the Sharing Preferences
section by selecting the 'Personal File Sharing' checkbox. 

Thereis a pre-authentication remotely exploitable stack buffer
overflow that allows an attacker to obtain administrative
privileges. The overflow occurs when parsing the PathName argument
from LoginExt packet requesting authentication using the Cleartext
Password User Authentication Method (UAM).  The PathName argument
is encoded as one-byte specifying the string type, two-bytes
specifying the string length, and finally the string itself.  A
string of type AFPName (0x3) that is longer than the length declared
in the packet will overflow the fixed-size stack buffer.

The previously described malformed request results in a trivially
exploitable stack buffer overflow.  @stake was able to quickly
develop a proof-of-concept exploit that portably demonstrates this
vulnerability across multiple Mac OS X versions including Mac OS X
10.3.3, 10.3.2, and 10.2.8.


Vendor Response:

- From APPLE-SA-2004-05-03 Security Update 2004-05-03

AppleFileServer: Fixes CAN-2004-0430 to improve the handling of long
passwords. Credit to Dave G. from @stake for reporting this issue.

Security Update 2004-05-03 may be obtained from:

  * Software Update pane in System Preferences

  * Apple's Software Downloads web site:

    For Mac OS X 10.3.3 "Panther"
    =============================
    http://download.info.apple.com/Mac_OS_X/061-1213.20040503.vngr3/
2Z/SecUpd2004-05-03Pan.dmg
    The download file is named: "SecUpd2004-05-03Pan.dmg"
    Its SHA-1 digest is: 6f35539668d80ee536305a4146bd982a93706532
   
    For Mac OS X Server 10.3.3
    ==========================
    http://download.info.apple.com/Mac_OS_X/061-1215.20040503.mPp9k/
2Z/SecUpdSrvr2004-05-03Pan.dmg
    The download file is named: "SecUpdSrvr2004-05-03Pan.dmg"
    Its SHA-1 digest is: 3c7da910601fd36d4cdfb276af4783ae311ac5d7
   
    For Mac OS X 10.2.8 "Jaguar"
    =============================
    http://download.info.apple.com/Mac_OS_X/061-1217.20040503.BmkY5/
2Z/SecUpd2004-05-03Jag.dmg
    The download file is named: "SecUpd2004-05-03Jag.dmg"
    Its SHA-1 digest is: 11d5f365e0db58b369d85aa909ac6209e2f49945
   
    For Mac OS X Server 10.2.8
    ==========================
    http://download.info.apple.com/Mac_OS_X/061-1219.20040503.Zsw3S/
2Z/SecUpdSrvr2004-05-03Jag.dmg
    The download file is named: "SecUpdSrvr2004-05-03Jag.dmg"
    Its SHA-1 digest is: 28859a4c88f6e1d1fe253388b233a5732b6e42fb


Timeline

3/26/2004 Vendor notified of issue
5/04/2004 Vendor informs us that they have a patch available
4/04/2004 Advisory released


Recommendation:

If you do not need AFS, disable it.  If you do need it, upgrade to
the latest version of Panther. 


Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned
the following names to these issues.  These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

  CAN-2004-0430  AppleFileServer Remote Command Execution


Open Source Vulnerability Database (OSVDB) Information:
More information available at www.osvdb.org

  OSVDB ID 5762


@stake Vulnerability Reporting Policy:
http://www.atstake.com/research/policy/

@stake Advisory Archive:
http://www.atstake.com/research/advisories/

PGP Key:
http://www.atstake.com/research/pgp_key.asc

Copyright 2004 @stake, Inc. All rights reserved.






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