Executive brief
A vulnerability in the BIND 9 DNS server software can allow a remote attacker to crash the service. BIND is a critical component used to translate human-readable domain names into IP addresses; if it fails, internet services, websites, and email delivery for the organization may become unavailable. This issue occurs when the server processes specifically formatted DNS messages that use non-standard data classes.
Technical details
Multiple flaws exist in the 'named' component of BIND 9 regarding the handling of DNS messages with CLASS values other than Internet (IN), such as CHAOS, HESIOD, ANY, or NONE. The root cause involves improper input validation and type confusion when these non-IN classes reach specific code paths including recursion, dynamic updates (UPDATE), and zone change notifications (NOTIFY). A remote, unauthenticated attacker can trigger an assertion failure by sending specially crafted DNS requests, leading to a daemon crash and denial of service. Both authoritative servers and resolvers are affected. Patches are available in versions 9.18.49, 9.20.23, and 9.21.22.
Affected products
- ISC BIND 9 9.11.0 through 9.16.50, 9.18.0 through 9.18.48, 9.20.0 through 9.20.22, 9.21.0 through 9.21.21
- ISC BIND 9 Supported Preview Edition 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.48-S1, 9.20.9-S1 through 9.20.22-S1
Timeline
- 2026-05-13: other: Early notification provided
- 2026-05-20: disclosed: Public disclosure and advisory published
- 2026-05-20: patched: Patched versions released