The code that processes control channel messages sent to `named` calls certain functions recursively during packet parsing. Recursion depth is only limited by the maximum accepted packet size; depending on the environment, this may cause the packet-parsing code to run out of available stack memory, causing `named` to terminate unexpectedly. Since each incoming control channel message is fully parsed before its contents are authenticated, exploiting this flaw does not require the attacker to hold a valid RNDC key; only network access to the control channel's configured TCP port is necessary. This issue affects BIND 9 versions 9.2.0 through 9.16.43, 9.18.0 through 9.18.18, 9.19.0 through 9.19.16, 9.9.3-S1 through 9.16.43-S1, and 9.18.0-S1 through 9.18.18-S1.

A `named` instance configured to run as a DNSSEC-validating recursive resolver with the Aggressive Use of DNSSEC-Validated Cache (RFC 8198) option (`synth-from-dnssec`) enabled can be remotely terminated using a zone with a malformed NSEC record. This issue affects BIND 9 versions 9.16.8-S1 through 9.16.41-S1 and 9.18.11-S1 through 9.18.15-S1.

Every `named` instance configured to run as a recursive resolver maintains a cache database holding the responses to the queries it has recently sent to authoritative servers. The size limit for that cache database can be configured using the `max-cache-size` statement in the configuration file; it defaults to 90% of the total amount of memory available on the host. When the size of the cache reaches 7/8 of the configured limit, a cache-cleaning algorithm starts to remove expired and/or least-recently used RRsets from the cache, to keep memory use below the configured limit. It has been discovered that the effectiveness of the cache-cleaning algorithm used in `named` can be severely diminished by querying the resolver for specific RRsets in a certain order, effectively allowing the configured `max-cache-size` limit to be significantly exceeded. This issue affects BIND 9 versions 9.11.0 through 9.16.41, 9.18.0 through 9.18.15, 9.19.0 through 9.19.13, 9.11.3-S1 through 9.16.41-S1, and 9.18.11-S1 through 9.18.15-S1.

BIND 9 resolver can crash when stale cache and stale answers are enabled, option `stale-answer-client-timeout` is set to a positive integer, and the resolver receives an RRSIG query. This issue affects BIND 9 versions 9.16.12 through 9.16.36, 9.18.0 through 9.18.10, 9.19.0 through 9.19.8, and 9.16.12-S1 through 9.16.36-S1.

Sending a flood of dynamic DNS updates may cause `named` to allocate large amounts of memory. This, in turn, may cause `named` to exit due to a lack of free memory. We are not aware of any cases where this has been exploited. Memory is allocated prior to the checking of access permissions (ACLs) and is retained during the processing of a dynamic update from a client whose access credentials are accepted. Memory allocated to clients that are not permitted to send updates is released immediately upon rejection. The scope of this vulnerability is limited therefore to trusted clients who are permitted to make dynamic zone changes. If a dynamic update is REFUSED, memory will be released again very quickly. Therefore it is only likely to be possible to degrade or stop `named` by sending a flood of unaccepted dynamic updates comparable in magnitude to a query flood intended to achieve the same detrimental outcome. BIND 9.11 and earlier branches are also affected, but through exhaustion of internal resources rather than memory constraints. This may reduce performance but should not be a significant problem for most servers. Therefore we don't intend to address this for BIND versions prior to BIND 9.16. This issue affects BIND 9 versions 9.16.0 through 9.16.36, 9.18.0 through 9.18.10, 9.19.0 through 9.19.8, and 9.16.8-S1 through 9.16.36-S1.

By spoofing the target resolver with responses that have a malformed EdDSA signature, an attacker can trigger a small memory leak. It is possible to gradually erode available memory to the point where named crashes for lack of resources.

By spoofing the target resolver with responses that have a malformed ECDSA signature, an attacker can trigger a small memory leak. It is possible to gradually erode available memory to the point where named crashes for lack of resources.

By flooding the target resolver with queries exploiting this flaw an attacker can significantly impair the resolver's performance, effectively denying legitimate clients access to the DNS resolution service.

BIND 9.11.0 -> 9.11.36 9.12.0 -> 9.16.26 9.17.0 -> 9.18.0 BIND Supported Preview Editions: 9.11.4-S1 -> 9.11.36-S1 9.16.8-S1 -> 9.16.26-S1 Versions of BIND 9 earlier than those shown - back to 9.1.0, including Supported Preview Editions - are also believed to be affected but have not been tested as they are EOL. The cache could become poisoned with incorrect records leading to queries being made to the wrong servers, which might also result in false information being returned to clients.

BIND 9.16.11 -> 9.16.26, 9.17.0 -> 9.18.0 and versions 9.16.11-S1 -> 9.16.26-S1 of the BIND Supported Preview Edition. Specifically crafted TCP streams can cause connections to BIND to remain in CLOSE_WAIT status for an indefinite period of time, even after the client has terminated the connection.

In BIND 9.3.0 -> 9.11.35, 9.12.0 -> 9.16.21, and versions 9.9.3-S1 -> 9.11.35-S1 and 9.16.8-S1 -> 9.16.21-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.18 of the BIND 9.17 development branch, exploitation of broken authoritative servers using a flaw in response processing can cause degradation in BIND resolver performance. The way the lame cache is currently designed makes it possible for its internal data structures to grow almost infinitely, which may cause significant delays in client query processing.

In BIND 9.5.0 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.11.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.1 of the BIND 9.17 development branch, BIND servers are vulnerable if they are running an affected version and are configured to use GSS-TSIG features. In a configuration which uses BIND's default settings the vulnerable code path is not exposed, but a server can be rendered vulnerable by explicitly setting values for the tkey-gssapi-keytab or tkey-gssapi-credential configuration options. Although the default configuration is not vulnerable, GSS-TSIG is frequently used in networks where BIND is integrated with Samba, as well as in mixed-server environments that combine BIND servers with Active Directory domain controllers. For servers that meet these conditions, the ISC SPNEGO implementation is vulnerable to various attacks, depending on the CPU architecture for which BIND was built: For named binaries compiled for 64-bit platforms, this flaw can be used to trigger a buffer over-read, leading to a server crash. For named binaries compiled for 32-bit platforms, this flaw can be used to trigger a server crash due to a buffer overflow and possibly also to achieve remote code execution. We have determined that standard SPNEGO implementations are available in the MIT and Heimdal Kerberos libraries, which support a broad range of operating systems, rendering the ISC implementation unnecessary and obsolete. Therefore, to reduce the attack surface for BIND users, we will be removing the ISC SPNEGO implementation in the April releases of BIND 9.11 and 9.16 (it had already been dropped from BIND 9.17). We would not normally remove something from a stable ESV (Extended Support Version) of BIND, but since system libraries can replace the ISC SPNEGO implementation, we have made an exception in this case for reasons of stability and security.

In BIND 9.0.0 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.9.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.11 of the BIND 9.17 development branch, when a vulnerable version of named receives a query for a record triggering the flaw described above, the named process will terminate due to a failed assertion check. The vulnerability affects all currently maintained BIND 9 branches (9.11, 9.11-S, 9.16, 9.16-S, 9.17) as well as all other versions of BIND 9.

In BIND 9.8.5 -> 9.8.8, 9.9.3 -> 9.11.29, 9.12.0 -> 9.16.13, and versions BIND 9.9.3-S1 -> 9.11.29-S1 and 9.16.8-S1 -> 9.16.13-S1 of BIND 9 Supported Preview Edition, as well as release versions 9.17.0 -> 9.17.11 of the BIND 9.17 development branch, when a vulnerable version of named receives a malformed IXFR triggering the flaw described above, the named process will terminate due to a failed assertion the next time the transferred secondary zone is refreshed.

BIND servers are vulnerable if they are running an affected version and are configured to use GSS-TSIG features. In a configuration which uses BIND's default settings the vulnerable code path is not exposed, but a server can be rendered vulnerable by explicitly setting valid values for the tkey-gssapi-keytab or tkey-gssapi-credentialconfiguration options. Although the default configuration is not vulnerable, GSS-TSIG is frequently used in networks where BIND is integrated with Samba, as well as in mixed-server environments that combine BIND servers with Active Directory domain controllers. The most likely outcome of a successful exploitation of the vulnerability is a crash of the named process. However, remote code execution, while unproven, is theoretically possible. Affects: BIND 9.5.0 -> 9.11.27, 9.12.0 -> 9.16.11, and versions BIND 9.11.3-S1 -> 9.11.27-S1 and 9.16.8-S1 -> 9.16.11-S1 of BIND Supported Preview Edition. Also release versions 9.17.0 -> 9.17.1 of the BIND 9.17 development branch

There had existed in one of the ISC BIND libraries a bug in a function that was used by dhcpd when operating in DHCPv6 mode. There was also a bug in dhcpd relating to the use of this function per its documentation, but the bug in the library function prevented this from causing any harm. All releases of dhcpd from ISC contain copies of this, and other, BIND libraries in combinations that have been tested prior to release and are known to not present issues like this. Some third-party packagers of ISC software have modified the dhcpd source, BIND source, or version matchup in ways that create the crash potential. Based on reports available to ISC, the crash probability is large and no analysis has been done on how, or even if, the probability can be manipulated by an attacker. Affects: Builds of dhcpd versions prior to version 4.4.1 when using BIND versions 9.11.2 or later, or BIND versions with specific bug fixes backported to them. ISC does not have access to comprehensive version lists for all repackagings of dhcpd that are vulnerable. In particular, builds from other vendors may also be affected. Operators are advised to consult their vendor documentation.