CVE-2015-8605: UDP payload length not properly checked

[Michael McNally]

CVE:                   CVE-2015-8605
Document Version:      2.0
Posting date:          12 January 2016
Program Impacted:      DHCP
Versions affected:     4.0.x, 4.1.x, 4.2.x, 4.1-ESV -> 4.1-ESV-R12,
                       4.3.0->4.3.3.  DHCP 3.x may also be affected
                       but has not been tested.
Severity:              Medium
Exploitable:           From adjacent networks

Description:

   A badly formed packet with an invalid IPv4 UDP length field can
   cause a DHCP server, client, or relay program to terminate
   abnormally.

Impact:

   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)

Workarounds:

   None likely, but in some environments following the advice from
   https://kb.isc.org/article/AA-00573/ can substantially reduce the
   risk by limiting the exposure of a DHCP server to "controlled"
   networks and clients.

Active exploits:

   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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Note:

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   be found here: https://kb.isc.org/article/AA-00861

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