Posting date: 12 January 2016
4.0.x, 4.1.x, 4.2.x, 4.1-ESV -> 4.1-ESV-R12, 4.3.0->4.3.3. 3.x may also be affected but has not been tested.
From adjacent networks
A badly formed packet with an invalid IPv4 UDP length field can cause a DHCP server, client, or relay program to terminate abnormally.
Nearly all IPv4 DHCP clients and relays, and most IPv4 DHCP servers are potentially affected.
A server, client, or relay that is built to only be able to process unicast packets (i.e. those that have already been processed by the OS UDP/IP stack) is not affected, however this build configuration is not normally viable for clients and relays. Servers with this build configuration require a relay in order to be able to process DISCOVER and other broadcast requests from clients.
Not all potentially-affected builds will actually be affected, but because it is difficult to identify or predict those which should be upgraded, our advice is that all builds should be considered vulnerable.
CVSS Score: 5.7
CVSS Vector: (AV:A/AC:M/Au:N/C:N/I:N/A:C)
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=(AV:A/AC:M/Au:N/C:N/I:N/A:C)
None likely, but in some environments following the advice from https://kb.isc.org/article/AA-00573/31/Securing-Your-Network-From-DHCP-Risks.html can substantially reduce the risk by limiting the exposure of a DHCP server to "controlled" networks and clients.
No known active exploits.
Solution: Upgrade to the patched release most closely related to your current version of DHCP. These can all be downloaded from http://www.isc.org/downloads.
- DHCP version 4.1-ESV-R12-P1
- DHCP version 4.3.3-P1
Acknowledgements: Thanks to
Sebastian Poehn from Sophos for reporting this issue.
Document Revision History:
1.0 Advance Notification 5 January, 2016
1.1 ESV Version name corrected 12 January 2016
2.0 Public Disclosure 12 January, 2016
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This Knowledge Base article https://kb.isc.org/article/AA-01334 is the complete and official security advisory document.
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