ISC Security Advisory: Memory Leaks Found in ISC DHCP

Cathy Almond cathya at
Tue Jul 24 17:54:44 UTC 2012

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Title: Memory Leaks Found In ISC DHCP


Two memory leaks have been found and fixed in ISC DHCP. Both are
reproducible when running in DHCPv6 mode (with the -6 command-line
argument.) The first leak is confirmed to only affect servers operating
in DHCPv6 mode, but based on initial code analysis the second may
theoretically affect DHCPv4 servers (though this has not been demonstrated.)

CVE: CVE-2012-3954
Document Version: 2.0
Posting date: 24 July 2012
Program Impacted: ISC DHCP 4
Versions affected: 4.1.x, 4.2.x
Severity: Medium
Exploitable: From networks permitted to send requests to the DHCP server.


ISC has discovered and fixed two memory leaks in the DHCP code. One of
the leaks only affects servers running in DHCPv6 mode. The other is
known to affect a server running in DHCPv6 mode but could potentially
occur on servers running in DHCPv4 mode as well. In both cases the
server can leak a small amount of memory while processing messages. The
amount leaked per iteration is small and the leak will not cause
problems in many cases. However on a server that is run for a long
period without re-starting or a server handling an extraordinary amount
of traffic from the clients the leak could consume all memory available
to the DHCP server process, preventing further operation by the DHCP
server process and potentially interfering with other services hosted on
the same server hardware.

Note: Under ISC's disclosure policy, this issue would not normally
require an advisory but we are issuing one in this case in coordination
with other security issues being disclosed at this time. DHCP 3.1-ESV
has not been tested for this issue but examination of the code suggests
that it is potentially vulnerable. All versions of ISC DHCP 3 are
currently beyond the end of their support from ISC and we will not be
releasing patches for these "End of Life" (EOL) versions.

CVSS Score: 3.3

CVSS Equation: (AV:A/AC:L/Au:N/C:N/I:N/A:P)

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


Restarting the server at periodic intervals will address the problem
sufficiently in most operational environments. Where DHCP traffic is
permitted from hosts not under the control of the network operator (e.g.
open or semi-public networks) upgrading is more strongly recommended.

Solution: Upgrade to ISC DHCP 4.1-ESV-R6 or 4.2.4-P1

Download 4.2.4-P1 or 4.1-ESV-R6 from

Exploit Status: No known active exploits

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

Document Revision History:

        1.0 - 11 July, 2012 - Phase 1 contacted
        1.1 - 17 July, 2012. - Phase 1 re-issued, re-released patch with
additional code
        1.2 - 23 July, 2012 - Phase 2 & 3 notification sent
        2.0 - 24 July, 2012 - Phase 4-Public release


- Do you have Questions? Questions regarding this advisory should go to
security-officer at

- ISC Security Vulnerability Disclosure Policy: Details of our current
security advisory policy and practice can be found

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