# CVE-2026-11721: ISC BIND 9 cache poisoning via RRSIG label count discrepancy

Source: https://junglewise.ai/threats/cve-2026-11721-isc-bind-9-cache-poisoning-via-rrsig-label-count-discrepancy  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-22. Updated: 2026-07-22  
License: CC BY 4.0 with a link back

CVE-2026-11721 · Severity: high · CVSS 7.5 · Published 2026-07-22

A vulnerability has been identified in BIND 9, a widely used software suite for managing the Domain Name System (DNS) on the internet. An attacker can trick the system into storing incorrect website address information in its memory, a process known as cache poisoning. This could allow an attacker to redirect users to malicious websites or disrupt normal internet traffic for organizations relying on the affected software.

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-2026-11721 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-11721 being exploited in the wild.

**How severe is CVE-2026-11721?** High severity, with a CVSS score of 7.5, published 22 July 2026.

**Which products and versions are affected?** Isc BIND 9 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23; Isc BIND 9 Supported Preview Edition 9.11.3-S1 through 9.18.50-S1, 9.20.9-S1 through 9.20.24-S1.

**Is there a fix for CVE-2026-11721?** A patch was published on 2026-07-22: Fixed versions released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-11721 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-11721?** 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

A vulnerability exists in BIND 9's handling of DNSSEC-signed responses where an attacker's zone can respond with an RRSIG record containing a smaller number of labels than the zone itself. This discrepancy causes the 'named' process to incorrectly produce a wildcard name for a zone shorter than the attacker's zone. This behavior facilitates cache poisoning, allowing an attacker to inject arbitrary DNS data into the resolver's cache. The vulnerability requires the 'synth-from-dnssec' option to be enabled, which is the default setting. Patches are available in versions 9.20.26, 9.21.24, and 9.20.26-S1.

## Affected products

- ISC BIND 9 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23
- ISC BIND 9 Supported Preview Edition 9.11.3-S1 through 9.18.50-S1, 9.20.9-S1 through 9.20.24-S1

## Timeline

- 2026-07-15: other: Early Notification
- 2026-07-22: advisory: Public disclosure
- 2026-07-22: patched: Fixed versions released

## References

- [https://downloads.isc.org/isc/bind9/9.20.26](https://downloads.isc.org/isc/bind9/9.20.26)
- [https://downloads.isc.org/isc/bind9/9.21.24](https://downloads.isc.org/isc/bind9/9.21.24)
- [https://kb.isc.org/docs/cve-2026-11721](https://kb.isc.org/docs/cve-2026-11721)

## 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 resource exhaustion in DNSSEC validating resolver](https://junglewise.ai/threats/cve-2026-11622-isc-bind-9-resource-exhaustion-in-dnssec-validating-resolver)