# CVE-2026-11721: Cache poisoning possible with label count discrepancy, RRSIG, and wildcards

> Attackers can poison the DNS cache of BIND resolvers by exploiting a label count discrepancy in RRSIGs, leading to incorrect data resolution.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Jul 2026
- **Updated:** 22 Jul 2026
- **Also known as:** ALPINE-CVE-2026-11721, AZL-93132, BELL-CVE-2026-11721, DEBIAN-CVE-2026-11721, ECHO-d56a-90b8-201c, GHSA-cq66-h8mj-77hh, MINI-3mxw-r6r9-w6wc, MINI-9frh-87j2-8jcx, MINI-mgq4-8mr3-792r, UBUNTU-CVE-2026-11721

## What is CVE-2026-11721?

CVE-2026-11721 is a high-severity vulnerability in ISC BIND 9, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

It is possible for an attacker's zone to respond to a query with an RRSIG that has a smaller number of labels than the zone in which the RRSIG is contained. This causes `named` to produce a wildcard name for a zone that is shorter than the attacker's zone, which can result in cache poisoning. For this attack to have any effect, the resolver under attack must have set `synth-from-dnssec yes;` (which is the default).
This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.

Weakness: CWE-1284 (Improper Validation of Specified Quantity in Input)

## Which versions are affected by CVE-2026-11721?


## How do I fix CVE-2026-11721?

Apply the vendor's patch.

## Is CVE-2026-11721 being exploited?

There is no known exploitation of CVE-2026-11721 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-11721 and fix it if it is affected.

What it is: CVE-2026-11721 is a high-severity vulnerability in ISC BIND 9, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-11721 in the wild and no public exploit code.

Affected product: ISC BIND 9. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-11721/ (Markdown: https://insights.sbomify.com/CVE-2026-11721/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-11721
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-11721
- OSV: https://osv.dev/vulnerability/CVE-2026-11721

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-11721/
Summaries are generated and may contain mistakes; the official description above is the record.