buffer.c in named in ISC BIND 9 before 9.9.9-P3, 9.10.x before 9.10.4-P3, and 9.11.x before 9.11.0rc3 does not properly construct responses, which allows remote attackers to cause a denial of service (assertion failure and daemon exit) via a crafted query.

ISC BIND 9.x before 9.9.9-P2, 9.10.x before 9.10.4-P2, and 9.11.x before 9.11.0b2, when lwresd or the named lwres option is enabled, allows remote attackers to cause a denial of service (daemon crash) via a long request that uses the lightweight resolver protocol.

Clients using DNS-over-HTTPS (DoH) can exhaust a DNS resolver's CPU and/or memory by flooding it with crafted valid or invalid HTTP/2 traffic. This issue affects BIND 9 versions 9.18.0 through 9.18.32, 9.20.0 through 9.20.4, 9.21.0 through 9.21.3, and 9.18.11-S1 through 9.18.32-S1.

It is possible to construct a zone such that some queries to it will generate responses containing numerous records in the Additional section. An attacker sending many such queries can cause either the authoritative server itself or an independent resolver to use disproportionate resources processing the queries. Zones will usually need to have been deliberately crafted to attack this exposure. This issue affects BIND 9 versions 9.11.0 through 9.11.37, 9.16.0 through 9.16.50, 9.18.0 through 9.18.32, 9.20.0 through 9.20.4, 9.21.0 through 9.21.3, 9.11.3-S1 through 9.11.37-S1, 9.16.8-S1 through 9.16.50-S1, and 9.18.11-S1 through 9.18.32-S1.

Client queries that trigger serving stale data and that also require lookups in local authoritative zone data may result in an assertion failure. This issue affects BIND 9 versions 9.16.13 through 9.16.50, 9.18.0 through 9.18.27, 9.19.0 through 9.19.24, 9.11.33-S1 through 9.11.37-S1, 9.16.13-S1 through 9.16.50-S1, and 9.18.11-S1 through 9.18.27-S1.

If a server hosts a zone containing a "KEY" Resource Record, or a resolver DNSSEC-validates a "KEY" Resource Record from a DNSSEC-signed domain in cache, a client can exhaust resolver CPU resources by sending a stream of SIG(0) signed requests. This issue affects BIND 9 versions 9.0.0 through 9.11.37, 9.16.0 through 9.16.50, 9.18.0 through 9.18.27, 9.19.0 through 9.19.24, 9.9.3-S1 through 9.11.37-S1, 9.16.8-S1 through 9.16.49-S1, and 9.18.11-S1 through 9.18.27-S1.

Resolver caches and authoritative zone databases that hold significant numbers of RRs for the same hostname (of any RTYPE) can suffer from degraded performance as content is being added or updated, and also when handling client queries for this name. This issue affects BIND 9 versions 9.11.0 through 9.11.37, 9.16.0 through 9.16.50, 9.18.0 through 9.18.27, 9.19.0 through 9.19.24, 9.11.4-S1 through 9.11.37-S1, 9.16.8-S1 through 9.16.50-S1, and 9.18.11-S1 through 9.18.27-S1.

A malicious client can send many DNS messages over TCP, potentially causing the server to become unstable while the attack is in progress. The server may recover after the attack ceases. Use of ACLs will not mitigate the attack. This issue affects BIND 9 versions 9.18.1 through 9.18.27, 9.19.0 through 9.19.24, and 9.18.11-S1 through 9.18.27-S1.

To keep its cache database efficient, `named` running as a recursive resolver occasionally attempts to clean up the database. It uses several methods, including some that are asynchronous: a small chunk of memory pointing to the cache element that can be cleaned up is first allocated and then queued for later processing. It was discovered that if the resolver is continuously processing query patterns triggering this type of cache-database maintenance, `named` may not be able to handle the cleanup events in a timely manner. This in turn enables the list of queued cleanup events to grow infinitely large over time, allowing the configured `max-cache-size` limit to be significantly exceeded. This issue affects BIND 9 versions 9.16.0 through 9.16.45 and 9.16.8-S1 through 9.16.45-S1.

If a resolver cache has a very large number of ECS records stored for the same name, the process of cleaning the cache database node for this name can significantly impair query performance. This issue affects BIND 9 versions 9.11.3-S1 through 9.11.37-S1, 9.16.8-S1 through 9.16.45-S1, and 9.18.11-S1 through 9.18.21-S1.