ISC BIND DoS Vulnerability (CVE-2021-25218) - Windows

ISC BIND is prone to a denial of service (DoS) vulnerability.

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 enabled. 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.

BIND version 9.16.19, 9.17.16 and 9.16.19-S1.

Checks if a vulnerable version is present on the target host.

Update to version 9.16.20, 9.17.17, 9.16.20-S1 or later.