# CVE-2026-3591: A stack use-after-return flaw in SIG(0) handling code may enable ACL bypass

> A stack use-after-return in BIND's SIG(0) handling allows attackers to bypass IP-based ACLs, potentially granting unauthorized access to DNS services.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Mar 2026
- **Updated:** 25 Mar 2026
- **Also known as:** ALPINE-CVE-2026-3591, AZL-80987, BELL-CVE-2026-3591, DEBIAN-CVE-2026-3591, GHSA-5fv2-2p94-9gh7, MINI-cmfx-9wr9-2pwv, UBUNTU-CVE-2026-3591

## What is CVE-2026-3591?

CVE-2026-3591 is a medium-severity use after free vulnerability in Isc Bind, published on 25 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A use-after-return vulnerability exists in the `named` server when handling DNS queries signed with SIG(0). Using a specially-crafted DNS request, an attacker may be able to cause an ACL to improperly (mis)match an IP address. In a default-allow ACL (denying only specific IP addresses), this may lead to unauthorized access. Default-deny ACLs should fail-secure.
This issue affects BIND 9 versions 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, and 9.20.9-S1 through 9.20.20-S1.
BIND 9 versions 9.18.0 through 9.18.46 and 9.18.11-S1 through 9.18.46-S1 are NOT affected.

Weakness: CWE-562 (Return of Stack Variable Address), CWE-305 (Authentication Bypass by Primary Weakness)

## Which versions are affected by CVE-2026-3591?

It affects 1 product.


Products: Isc Bind.

## How do I fix CVE-2026-3591?

Apply the vendor's patch.

## Is CVE-2026-3591 being exploited?

There is no known exploitation of CVE-2026-3591 in the wild and no public exploit code.

## Other vulnerabilities in Isc Bind

- [CVE-2008-0122](https://insights.sbomify.com/CVE-2008-0122/): Memory corruption in n/a (critical 10.0)
- [CVE-2001-0010](https://insights.sbomify.com/CVE-2001-0010/): Memory corruption in n/a (critical 10.0)
- [CVE-2001-0011](https://insights.sbomify.com/CVE-2001-0011/): Memory corruption in n/a (critical 10.0)
- [CVE-2001-0013](https://insights.sbomify.com/CVE-2001-0013/): Memory corruption in n/a (critical 10.0)
- [CVE-2000-1029](https://insights.sbomify.com/CVE-2000-1029/): Memory corruption in n/a (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-3591 and fix it if it is affected.

What it is: CVE-2026-3591 is a medium-severity use after free vulnerability in Isc Bind, published on 25 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-3591 in the wild and no public exploit code.

Affected product: Isc Bind. 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-2026-3591/ (Markdown: https://insights.sbomify.com/CVE-2026-3591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-3591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3591
- OSV: https://osv.dev/vulnerability/CVE-2026-3591

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-3591/
Summaries are generated and may contain mistakes; the official description above is the record.