Undefined behavior may result due to a race condition leading to a use-after-free violation. If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature. If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message.
This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1.
BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.

Project Subscriptions

Vendors Products
Advisories
Source ID Title
Debian DSA Debian DSA DSA-6285-1 bind9 security update
Ubuntu USN Ubuntu USN USN-8293-1 Bind vulnerabilities
Fixes

Solution

Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.23, 9.21.22, or 9.20.23-S1.


Workaround

No workarounds known.

History

Fri, 22 May 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-367
References
Metrics threat_severity

None

threat_severity

Important


Thu, 21 May 2026 15:30:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*

Wed, 20 May 2026 14:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 20 May 2026 13:15:00 +0000

Type Values Removed Values Added
Description Undefined behavior may result due to a race condition leading to a use-after-free violation. If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature. If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.
Title SIG(0) validation during query flood may lead to undefined behavior
First Time appeared Isc
Isc bind
Weaknesses CWE-362
CWE-416
CPEs cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*
Vendors & Products Isc
Isc bind
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: isc

Published:

Updated: 2026-05-20T13:39:38.654Z

Reserved: 2026-04-09T06:40:58.672Z

Link: CVE-2026-5947

cve-icon Vulnrichment

Updated: 2026-05-20T13:39:19.676Z

cve-icon NVD

Status : Analyzed

Published: 2026-05-20T13:16:40.303

Modified: 2026-05-21T15:24:32.997

Link: CVE-2026-5947

cve-icon Redhat

Severity : Important

Publid Date: 2026-05-21T12:15:50Z

Links: CVE-2026-5947 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-05-22T02:30:16Z

Weaknesses