CVE-2026-3591

A stack use-after-return flaw in SIG(0) handling code may enable ACL bypass

State: Published
Severity: 5.4 Medium
Published: Mar 25, 2026
Updated: Mar 25, 2026
Reserved: Mar 5, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	5.4 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N	isc

Weaknesses

CWE-562 Return of Stack Variable Address
CWE-305 Authentication Bypass by Primary Weakness

Affected Products

Product	Versions
BIND 9ISC	9.20.0 through 9.20.20Affected 9.21.0 through 9.21.19Affected 9.20.9-S1 through 9.20.20-S1Affected 9.18.0 through 9.18.46Not affected 9.18.11-S1 through 9.18.46-S1Not affected

References

CVE-2026-3591vendor-advisory
https://downloads.isc.org/isc/bind9/9.20.21patch
https://downloads.isc.org/isc/bind9/9.21.20patch

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