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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.

PUBLISHED Reserved 2026-03-05 | Published 2026-03-25 | Updated 2026-03-25 | Assigner isc




MEDIUM: 5.4CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Problem types

CWE-562 Return of Stack Variable Address

CWE-305 Authentication Bypass by Primary Weakness

Product status

Default status
unaffected

9.20.0 (custom)
affected

9.21.0 (custom)
affected

9.20.9-S1 (custom)
affected

9.18.0 (custom)
unaffected

9.18.11-S1 (custom)
unaffected

Credits

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

References

kb.isc.org/docs/cve-2026-3591 (CVE-2026-3591) vendor-advisory

downloads.isc.org/isc/bind9/9.20.21 patch

downloads.isc.org/isc/bind9/9.21.20 patch

cve.org (CVE-2026-3591)

nvd.nist.gov (CVE-2026-3591)

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