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

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Article Summary



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

Related Documents:

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Do you still have questions?   Questions regarding this advisory should go to

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

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This Knowledge Base article is the complete and official security advisory document.  There is also a summary article located on our website and linking to here:

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