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               Technical Cyber Security Alert TA04-174A
                Multiple Vulnerabilities in ISC DHCP 3

   Original release date: June 22, 2004
   Last revised: --
   Source: US-CERT

Systems Affected

     * ISC DHCP versions 3.0.1rc12 and 3.0.1rc13

Overview

   Two vulnerabilities in the ISC DHCP allow a remote attacker to cause a
   denial of the DHCP service on a vulnerable system. It may be possible
   to exploit these vulnerabilities to execute arbitrary code on the
   system.

I. Description

   As described in RFC 2131, "the Dynamic Host Configuration Protocol
   (DHCP) provides a framework for passing configuration information to
   hosts on a TCP/IP network." The Internet Systems Consortium's (ISC)
   Dynamic Host Configuration Protocol (DHCP) 3 application contains two
   vulnerabilities that present several potential buffer overflow
   conditions.

   VU#317350 discusses a buffer overflow vulnerability in the temporary
   storage of log lines. In transactions, ISC DHCPD logs every DHCP
   packet along with several pieces of descriptive information. The
   client's DISCOVER and the resulting OFFER, REQUEST, ACK, and NAKs are
   all logged. In all of these messages, if the client supplied a
   hostname, then it is also included in the logged line. As part of the
   DHCP datagram format, a client may specify multiple hostname options,
   up to 255 bytes per option. These options are concatenated by the
   server. If the hostname and options contain only ASCII characters,
   then the string will pass non-ASCII character filters and be
   temporarily stored in 1024 byte fixed-length buffers on the stack. If
   a client supplies enough hostname options, it is possible to overflow
   the fixed-length buffer.

   VU#654390 discusses C include files for systems that do not support
   the bounds checking vsnprintf() function. These files define the
   bounds checking vsnprintf() to the non-bounds checking vsprintf()
   function. Since vsprintf() is a function that does not check bounds,
   the size is discarded, creating the potential for a buffer overflow
   when client data is supplied. Note that the vsnprintf() statements are
   defined after the vulnerable code that is discussed in VU#317350.
   Since the preconditions for this vulnerability are similar to those
   required to exploit VU#317350, these buffer overflow conditions occur
   sequentially in the code after the buffer overflow vulnerability
   discussed in VU#317350, and these issues were discovered and resolved
   at the same time, there is no known exploit path to exploit these
   buffer overflow conditions caused by VU#654390. Note that VU#654390
   was discovered and exploitable once VU#317350 was resolved.

   For both of the vulnerabilities, only ISC DHCP 3.0.1rc12 and ISC DHCP
   3.0.1rc13 are believed to be vulnerable. VU#317350 is exploitable for
   all operating systems and configurations. VU#654390 is only defined
   for the following operating systems:

     * AIX
     * AlphaOS
     * Cygwin32
     * HP-UX
     * Irix
     * Linux
     * NextStep
     * SCO
     * SunOS 4
     * SunOS 5.5
     * Ultrix

   All versions of ISC DCHP 3, including all snapshots, betas, and
   release candidates, contain the flawed code. However, versions other
   than ISC DHCP 3.0.1rc12 and ISC DHCP 3.0.1rc13 discard all but the
   last hostname option provided by the client, so it is not believed
   that these versions are exploitable.

   US-CERT is tracking these issues as VU#317350, which has been assigned
   CVE CAN-2004-0460, and VU#654390, which has been assigned CVE
   CAN-2004-0461.

II. Impact

   Exploitation of these vulnerabilities may cause a denial-of-service
   condition to the DHCP daemon (DHCPD) and may permit a remote attacker
   to execute arbitrary code on the system with the privileges of the
   DHCPD process, typically root.

III. Solution

   Apply patches or upgrade

   These issues have been resolved in ISC DHCP 3.0.1rc14. Your vendor may
   provide specific patches or updates. For vendor-specific information,
   please see your vendor's site, or look for your vendor infomation in
   VU#317350 and VU#654390. As vendors report new information to US-CERT,
   we will update the vulnerability notes.

Appendix B. References

     * http://www.isc.org/sw/dhcp/
     * http://www.kb.cert.org/vuls/id/317350
     * http://www.kb.cert.org/vuls/id/654390
   _________________________________________________________________

   US-CERT thanks Gregory Duchemin and Solar Designer for discovering,
   reporting, and resolving this vulnerability. Thanks also to David
   Hankins of ISC for notifying us of this vulnerability and the
   technical information provided to create this document.
  _________________________________________________________________

   Feedback can be directed to the author: Jason A. Rafail
  _________________________________________________________________

   The latest version of this document can be found at:
     
     <http://www.us-cert.gov/cas/techalerts/TA04-174A.html>
  _________________________________________________________________
     
   Copyright 2004 Carnegie Mellon University.
     
   Terms of use:
     
     <http://www.us-cert.gov/legal.html>
   
  _________________________________________________________________

   Revision History

   June 22, 2004: Initial release

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