CVE-2026-3591

MEDIUM 5.4

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

CVSS Score

5.4

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-562 CWE-305
Vendor	isc
Product	bind 9
Published	Mar 25, 2026
Last Updated	Mar 25, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

ISC / BIND 9

9.20.0 ≤ 9.20.20 9.21.0 ≤ 9.21.19 9.20.9-S1 ≤ 9.20.20-S1

References

NVD ↗ CVE.org ↗ EPSS Data ↗

kb.isc.org: https://kb.isc.org/docs/cve-2026-3591 downloads.isc.org: https://downloads.isc.org/isc/bind9/9.20.21 downloads.isc.org: https://downloads.isc.org/isc/bind9/9.21.20

Credits

ISC would like to thank Mcsky23 for bringing this vulnerability to our attention.