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Bug 808909 (CVE-2021-25218) - net-dns/bind: Denial of service (CVE-2021-25218)
Summary: net-dns/bind: Denial of service (CVE-2021-25218)
Alias: CVE-2021-25218
Product: Gentoo Security
Classification: Unclassified
Component: Vulnerabilities (show other bugs)
Hardware: All Linux
: Normal normal (vote)
Assignee: Gentoo Security
Whiteboard: B3
Depends on:
Reported: 2021-08-18 18:03 UTC by Sam James
Modified: 2021-08-18 18:04 UTC (History)
2 users (show)

See Also:
Package list:
Runtime testing required: ---


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Description Sam James archtester Gentoo Infrastructure gentoo-dev Security 2021-08-18 18:03:40 UTC
If named attempts to respond over UDP with a response that is
  larger than the current effective interface maximum transmission
  unit (MTU), and if response-rate limiting (RRL) is active, an
  assertion failure is triggered (resulting in termination of the
  named server process).

  There are two ways for named to exceed the interface MTU:
  Direct configuration in named.conf setting max-udp-size to a
  value larger than the interface's MTU, or Path MTU discovery
  (PMTUD) informing the IP stack that it should use a smaller MTU
  for the interface and destination than the default max-udp-size
  value of 1232. Some operating systems allow packets received via
  other protocols to affect PMTUD values for DNS over UDP.

  While RRL is not enabled by default for user-defined views or
  the built-in default INTERNET (IN) class view, "_default", the
  built-in default CHAOS (CH) class view, "_bind", does have RRL

  Note that while this defect can be triggered through misconfiguration
  or by deliberate exploitation, it can also arise during normal
  operating conditions, even with hardened PMTUD settings.


  When a vulnerable version of named receives a query under the
  circumstances described above, the named process will terminate
  due to a failed assertion check.

  The vulnerability ONLY affects BIND 9 releases 9.16.19, 9.17.16,
  and release 9.16.19-S1 of the BIND Supported Preview Edition.
Comment 1 Sam James archtester Gentoo Infrastructure gentoo-dev Security 2021-08-18 18:04:41 UTC
No affected versions in ::gentoo.