Security Advisory - DHCP Regular Expressions Segfault

Summary:

Segmentation fault from dhcpd while processing an evaluated regular expression

CVE:

CVE-2011-4539

Document Version:

1.2

Posting date:

07 Dec 2011

Program Impacted:

DHCP

Versions affected:

4.0.x and higher, including all EOL versions back to 4.0, 4.1-ESV, and 4.2.x

Severity:

Medium

Exploitable:

remotely

Description:

A bug exists which allows an attacker who is able to send DHCP Request packets, either directly or through a relay, to remotely crash an ISC DHCP server if that server is configured to evaluate expressions using a regular expression (i.e. uses the "~=" or "~~" comparison operators.)

Further details are being withheld to allow administrators of affected systems time to patch. You are potentially vulnerable if you use regular expression comparison operators in your dhcpd.conf.

CVSS Score: 6.1

CVSS Equation: AV:

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:

http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2&vector=(tbd)

Workarounds:

This bug cannot be triggered if you are not using regular expressions in your configuration file.

Active exploits:

None known at this time.

Solution:

Upgrade to 4.1-ESV-R4 or 4.2.3-P1

Download patched versions from the following location: http://www.isc.org/software/dhcp

Acknowledgment:
Thank you to BlueCat Networks for finding and testing the issue.

Document Revision History

1.0 30 November 2011 - Phase I notified

1.1 6 December 2011 - Phase II & III notified

1.2 7 December 2011 - Public Release

Related Document:

References:

- Do you have Questions? Questions regarding this advisory should
go to security-officer@isc.org.

- ISC Security Vulnerability Disclosure Policy: Details of our
current security advisory policy and practice can be found here:
https://www.isc.org/security-vulnerability-disclosure-policy

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