# CVE-2026-5946: ISC BIND 9 denial of service in named via non-IN DNS classes

Source: https://junglewise.ai/threats/cve-2026-5946-isc-bind-9-denial-of-service-in-named-via-non-in-dns-classes  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-20. Updated: 2026-05-20  
License: CC BY 4.0 with a link back

CVE-2026-5946 · Severity: high · CVSS 7.5 · Published 2026-05-20

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.

Technologies: [Isc BIND 9](https://junglewise.ai/threats/technologies/bind-9), [Isc BIND 9 Supported Preview Edition](https://junglewise.ai/threats/technologies/bind-9-supported-preview-edition). Vendors: [Isc](https://junglewise.ai/threats/vendors/isc).

## Quick answers

**Is CVE-2026-5946 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-5946 being exploited in the wild.

**How severe is CVE-2026-5946?** High severity, with a CVSS score of 7.5, published 20 May 2026.

**Which products and versions are affected?** 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.

**Is there a fix for CVE-2026-5946?** A patch was published on 2026-05-20: Patched versions released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-5946 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-5946?** Check whether you run Isc BIND 9 or Isc BIND 9 Supported Preview Edition at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## 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

## References

- [https://downloads.isc.org/isc/bind9/9.18.49](https://downloads.isc.org/isc/bind9/9.18.49)
- [https://downloads.isc.org/isc/bind9/9.20.23](https://downloads.isc.org/isc/bind9/9.20.23)
- [https://downloads.isc.org/isc/bind9/9.21.22](https://downloads.isc.org/isc/bind9/9.21.22)
- [https://kb.isc.org/docs/cve-2026-5946](https://kb.isc.org/docs/cve-2026-5946)

## Related threats

- [ISC BIND recursive server assert failure denial of service](https://junglewise.ai/threats/cve-2026-97313-a-recursive-bind-server-that-receives-a-query-with-recursion)
- [ISC BIND DNSSEC validation bypass in NSEC records](https://junglewise.ai/threats/cve-2026-13321-isc-bind-dnssec-validation-bypass-in-nsec-records)
- [ISC BIND 9 denial of service via NSEC and NSEC3 assertion failure](https://junglewise.ai/threats/cve-2026-13204-isc-bind-9-denial-of-service-via-nsec-and-nsec3-assertion-failure)
- [ISC BIND 9 denial of service via CNAME or DNAME record ordering](https://junglewise.ai/threats/cve-2026-12617-isc-bind-9-denial-of-service-via-cname-or-dname-record-ordering)
- [ISC BIND 9 cache poisoning via RRSIG label count discrepancy](https://junglewise.ai/threats/cve-2026-11721-isc-bind-9-cache-poisoning-via-rrsig-label-count-discrepancy)