DHCP Vuln // no code 0day // Jun 22 2004 10:40PM
System Administrator (lowdownhaxor hotmail com)
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


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

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

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:

* AlphaOS
* Cygwin32
* Irix
* Linux
* NextStep
* 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

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
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