CVE-2012-3955: Reducing the expiration time for an IPv6 lease may cause the server to crash


Document Version:          
Posting date: 
12 September 2012
Program Impacted: 
Versions affected: 
4.1.x, 4.2.x
From networks permitted to send requests to the DHCP server.


ISC has discovered that reducing the expiration time for an active IPv6 lease may cause the server to crash.

Please Note: Versions of ISC DHCP 4.0 may also be affected, but these branches are beyond their "end of life" (EOL) and no longer receive testing or security fixes from ISC. For current information on which versions are actively supported, please see


Affected servers can terminate unexpectedly, resulting in a denial of service condition for clients.

CVSS Score:  5.7

CVSS Equation:  (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:


ISC recommends setting a value for the default-lease-time option in the configuration file, and not reducing it once set.

Active exploits:

No known active exploits.

Solution:  Upgrade to the updated release most closely related to your current version of DHCP.  These can be downloaded from

  • ISC DHCP version 4.1-ESV-R7
  • ISC DHCP version 4.2.4-P2

Acknowledgements: ISC would like to thank Glen Eustace of Massey University, New Zealand for finding this issue.

Document Revision History:

1.0 - 4 Sept. 2012 Advance Notification to Phase 1
1.1 - 11 Sept. 2012 Phase 2 & 3 notified
2.0 - 12 Sept. 2012 Phase 4 - Public Released

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