Knowledge Base ISC Main Website Ask a Question/Contact ISC
CVE-2009-1892: DHCP host record fenceposting error
Author: Cathy Almond Reference Number: AA-00963 Views: 2916 Created: 2013-05-29 14:35 Last Updated: 2013-05-30 12:05 0 Rating/ Voters

Versions of ISC dhcpd from 3.0.3 and onward have a fenceposting error that causes it to exit if it observes a DHCP client that matches two host records - one by DHCP Client Identifier option, the other by hardware address.

CVE: 
CVE-2009-1892  
Posting date: 
07 Oct 2009
Program Impacted: 
DHCP
Versions affected: 
3.0.3 and higher
Severity: 
Minor
Exploitable: 
Remotely with "local knowledge"

Description:

Theoretically, an attacker can cause the DHCP server to exit (and perform a Denial Of Service) by crafting a DHCP message that contains a specific CHADDR (hardware address) and DHCP Client Identifier option contents to match existing host records. However, using combinations of 'uid' and 'hardware' matching host records is not common configuration - generally either 'hardware' or 'uid' are used exclusively, rather than in mixtures. Furthermore, for the attack to be practical, the attacker would need to know the contents of the DHCP server's configuration file before the attack, something that DHCP Server Administrators do not frequently share. Although one could search through trial and error for the existence of such records in the DHCP server, the attacker would have to try every combination of perceived Client Identifiers and MAC Addresses, or to search those spaces through brute force. At this point it is both more practical and less server-implementation or configuration specific to simply use known DHCP protocol limitations to effect a DOS; such as forcibly allocating all addresses on the network.

Workarounds:

Temporarily convert existing "host {}" records to use 'hardware' match criteria exclusively.

Active exploits:

None known at this time.

Solution: 

Upgrade to 3.1.3, 4.0.2b2, 4.1.1b2, or later.

Related Documents:

If you'd like more information on our Forum or product support please visit www.isc.org/support.

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

Note: ISC patches only currently supported versions. When possible we indicate EOL versions affected.

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

This Knowledge Base article https://kb.isc.org/article/AA-00963 is the complete and official security advisory document.

Legal Disclaimer:
Internet Systems Consortium (ISC) is providing this notice on an "AS IS" basis. No warranty or guarantee of any kind is expressed in this notice and none should be implied. ISC expressly excludes and disclaims any warranties regarding this notice or materials referred to in this notice, including, without limitation, any implied warranty of merchantability, fitness for a particular purpose, absence of hidden defects, or of non-infringement. Your use or reliance on this notice or materials referred to in this notice is at your own risk. ISC may change this notice at any time.  A stand-alone copy or paraphrase of the text of this document that omits the document URL is an uncontrolled copy. Uncontrolled copies may lack important information, be out of date, or contain factual errors.


© 2001-2017 Internet Systems Consortium

For assistance with problems and questions for which you have not been able to find an answer in our Knowledge Base, we recommend searching our community mailing list archives and/or posting your question there (you will need to register there first for your posts to be accepted). The bind-users and the dhcp-users lists particularly have a long-standing and active membership.

ISC relies on the financial support of the community to fund the development of its open source software products. If you would like to support future product evolution and maintenance as well having peace of mind knowing that our team of experts are poised to provide you with individual technical assistance whenever you call upon them, then please consider our Professional Subscription Support services - details can be found on our main website.

Feedback
  • There is no feedback for this article
Quick Jump Menu