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.
No affected versions in ::gentoo.