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

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Summary

CVECVE-2026-3591
StatePUBLISHED
Assignerisc
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-25 14:16:37 UTC
Updated2026-05-21 15:24:36 UTC
DescriptionA 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.

Risk And Classification

Primary CVSS: v3.1 5.4 MEDIUM from [email protected]

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

Problem Types: CWE-305 | CWE-562 | CWE-562 CWE-562 Return of Stack Variable Address | CWE-305 CWE-305 Authentication Bypass by Primary Weakness

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.4MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
3.1CNADECLARED5.4MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Isc Bind All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA ISC BIND 9 affected 9.20.0 9.20.20 custom Not specified
CNA ISC BIND 9 affected 9.21.0 9.21.19 custom Not specified
CNA ISC BIND 9 affected 9.20.9-S1 9.20.20-S1 custom Not specified
CNA ISC BIND 9 unaffected 9.18.0 9.18.46 custom Not specified
CNA ISC BIND 9 unaffected 9.18.11-S1 9.18.46-S1 custom Not specified

References

ReferenceSourceLinkTags
downloads.isc.org/isc/bind9/9.20.21 [email protected] downloads.isc.org Patch
downloads.isc.org/isc/bind9/9.21.20 [email protected] downloads.isc.org Patch
kb.isc.org/docs/cve-2026-3591 [email protected] kb.isc.org Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: ISC would like to thank Mcsky23 for bringing this vulnerability to our attention. (en)

Additional Advisory Data

Solutions

CNA: Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.21, 9.21.20, or 9.20.21-S1.

Workarounds

CNA: No workarounds known.

Exploits

CNA: We are not aware of any active exploits.

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