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

CVE-2026-3591 is fixed in 6 products on 1 platform, first by DEBIAN-CVE-2026-3591, released March 25, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-3591
- Priority: Routine
- CVSS: 5.4 (Moderate)
- EPSS: 0.0037
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 24, 2026
- Weakness: Return of Stack Variable Address
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-3591

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | bind opensuse-leap 16.0 | 9.20.21-160000.1.1 | [OPENSUSE-SU-2026:20550-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-20550-1.md) | Apr 16, 2026 |
| Linux | bind sles 15.7 | 9.20.21-150700.3.18.1 | [SUSE-SU-2026:1351-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-1351-1.md) | Apr 15, 2026 |
| Linux | bind sles 16.0 | 9.20.21-160000.1.1 | [SUSE-SU-2026:21204-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-21204-1.md) | Apr 16, 2026 |
| Linux | bind9 Debian 13.5 (trixie) | 1:9.20.21-1~deb13u1 | [DEBIAN-CVE-2026-3591](https://patchblox.com/security/data/fix/linux/debian-cve-2026-3591.md) | Mar 25, 2026 |
| Linux | bind9 Debian 14 | 1:9.20.21-1 | [DEBIAN-CVE-2026-3591](https://patchblox.com/security/data/fix/linux/debian-cve-2026-3591.md) | Mar 25, 2026 |
| Linux | bind9 Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.2 | [bind9 1:9.20.11-1ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-bind9-1-9.20.11-1ubuntu2.2.md) | Apr 15, 2026 |
| Linux | bind9-dnsutils Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.2 | [bind9-dnsutils 1:9.20.11-1ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-bind9-dnsutils-1-9.20.11-1ubuntu2.2.md) | Apr 15, 2026 |
| Linux | bind9-host Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.2 | [bind9-host 1:9.20.11-1ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-bind9-host-1-9.20.11-1ubuntu2.2.md) | Apr 15, 2026 |
| Linux | bind9-libs Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.2 | [bind9-libs 1:9.20.11-1ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-bind9-libs-1-9.20.11-1ubuntu2.2.md) | Apr 15, 2026 |
| Linux | bind9-utils Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.2 | [bind9-utils 1:9.20.11-1ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-questing-bind9-utils-1-9.20.11-1ubuntu2.2.md) | Apr 15, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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