CVE-2026-5946: Invalid handling of CLASS != IN

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-20 · updated 2026-09-17
Weakness: CWE-20

Description

Multiple flaws have been identified in `named` related to the handling of DNS messages whose CLASS is not Internet (`IN`) — for example, `CHAOS` or `HESIOD`, or DNS messages that specify meta-classes (`ANY` or `NONE`) in the question section. Specially crafted requests reaching the affected code paths — recursion, dynamic updates (`UPDATE`), zone change notifications (`NOTIFY`), or processing of `IN`-specific record types in non-`IN` data — can cause assertion failures in `named`. This issue affects BIND 9 versions 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, 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.48-S1, and 9.20.9-S1 through 9.20.22-S1.

Affected products

ISC BIND: from 9.11.0 through 9.16.50; from 9.18.0 before 9.18.49; from 9.20.0 before 9.20.23; from 9.21.0 before 9.21.22 — fixed in 9.18.49, 9.20.23, 9.21.22

How to fix

Upgrade to a fixed version: ISC BIND 9.18.49, 9.20.23, 9.21.22. Check the vendor advisory for mitigations.

References

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