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.

How to fix CVE-2026-3591

To remediate CVE-2026-3591, upgrade the affected package to a fixed version below.

• —upgrade to 9.20.21-r0 or later
• —upgrade to 1:9.20.21-1~deb13u1 or later

Is CVE-2026-3591 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 9.20.21-r0
• from 0, < 1:9.20.21-1~deb13u1

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2026-3591
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-3591