CVE-2018-5737: BIND 9.12's serve-stale implementation can cause an assertion failure in rbtdb.c or other undesirable behavior, even if serve-stale is not enabled.

Michael McNally mcnally at
Fri May 18 19:06:21 UTC 2018

CVE:                 CVE-2018-5737
Document Version:    2.0
Posting date:        18 May 2018
Program Impacted:    BIND
Versions affected:   9.12.0, 9.12.1
Severity:            Medium
Exploitable:         Remotely


   A problem with the implementation of the new serve-stale feature
   in BIND 9.12 can lead to an assertion failure in rbtdb.c, even
   when stale-answer-enable is off.  Additionally, problematic
   interaction between the serve-stale feature and NSEC aggressive
   negative caching can in some cases cause undesirable behavior
   from named, such as a recursion loop or excessive logging.

   Deliberate exploitation of this condition could cause operational
   problems depending on the particular manifestation -- either
   degradation or denial of service.


   Servers running a vulnerable version of BIND (9.12.0, 9.12.1)
   which permit recursion to clients and which have the max-stale-ttl
   parameter set to a non-zero value are at risk.

CVSS Score:          5.9
CVSS Vector:         CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

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


   Setting "max-stale-ttl 0;" in named.conf will prevent exploitation
   of this vulnerability (but will effectively disable the serve-stale

   Setting "stale-answer enable off;" is not sufficient to prevent
   exploitation, max-stale-ttl needs to be set to zero.

Active exploits:

   No known active exploits.


   The error which can be exploited in this vulnerability is present
   in only two public release versions of BIND, 9.12.0 and 9.12.1.
   If you are running an affected version then upgrade to BIND


   ISC would like to thank Tony Finch of the University of Cambridge
   for his assistance in discovering and analyzing this vulnerability.

Document Revision History:

   1.0 Advance Notification, 09 May 2018
   1.1 BIND 9.12.1-P1 was recalled before public announcement
       due to defect, the advisory language was re-written to be
       clearer about the exploit risk, and the public disclosure
       date was adjusted because of the problem with 9.12.1-P1,
       17 May 2018
   2.0 Public Disclosure, 18 May 2018

Related Documents:

   See our BIND9 Security Vulnerability Matrix at for a complete listing of
   Security Vulnerabilities and versions affected.

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