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Alert (TA04-174A)

Multiple Vulnerabilities in ISC DHCP 3

Systems Affected

  • ISC DHCP versions 3.0.1rc12 and 3.0.1rc13


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.


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.


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.


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 A. References

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

Revision History

  • June 22, 2004: Initial release

    Last updated

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