CVE-2026-3591

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

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.

Affected Products

Vendor	Product	Versions
ISC	BIND 9	9.20.0, 9.21.0, 9.20.9-S1, 9.18.45, 9.21.20

References

https://kb.isc.org/docs/cve-2026-3591(vendor-advisory)
https://downloads.isc.org/isc/bind9/9.20.21(patch)
https://downloads.isc.org/isc/bind9/9.21.20(patch)

Related News (2 articles)

Tier C

oss-security2h ago

ISC has disclosed four vulnerabilities in BIND 9 (CVE-2026-1519, CVE-2026-3104, CVE-2026-3119, CVE-2026-3591)

→ No new info (linked only)

Tier C

VulDB3h ago

CVE-2026-3591 | ISC BIND prior 9.20.21/9.21.20 named return of stack variable address

→ No new info (linked only)

CVSS 3.15.4 CRITICAL

VectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CISA KEV❌ No

Actively exploited✅ Yes

CWECWE-562, CWE-305

Published3/25/2026

Last enriched2h agov2

Trending Score51

Source articles3

Independent2

Info Completeness9/14

Missing: epss, kev, exploit, iocs, mitre_attack

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Verification

State: unverified

Confidence: 0%

Version History

Last enriched 2h ago

v2Tier C2h ago

Updated severity to CRITICAL, added new affected versions, and noted that the vulnerability is actively exploited.

severityaffectedVersionsactivelyExploitedpatchAvailable

via VulDB

v13h ago

Initial creation