CVE-2026-5947

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://downloads.isc.org/isc/bind9/9.20.23	Patch
https://downloads.isc.org/isc/bind9/9.21.22	Patch
https://kb.isc.org/docs/cve-2026-5947	Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:7412
https://access.redhat.com/security/cve/CVE-2026-5947
https://bugzilla.redhat.com/show_bug.cgi?id=2479772
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:isc:bind:::::-:::*
	cpe:2.3:a:isc:bind:::::-:::*

History

No history.

Information

Published : 2026-05-20 13:16

Updated : 2026-08-24 13:19

NVD link : CVE-2026-5947

Mitre link : CVE-2026-5947

CVE.ORG link : CVE-2026-5947

JSON object : View

Products Affected

isc

bind

CWE

CWE-362

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CWE-416

Use After Free

CWE-367

Time-of-check Time-of-use (TOCTOU) Race Condition

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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.\nThis 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.\nBIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected."}, {"lang": "es", "value": "El comportamiento indefinido puede resultar debido a una condici\u00f3n de carrera que lleva a una violaci\u00f3n de uso despu\u00e9s de liberaci\u00f3n. Si BIND recibe un mensaje DNS entrante firmado con SIG(0), comienza a trabajar para validar esa firma. Si, durante esa validaci\u00f3n, se alcanza el l\u00edmite de 'recursive-clients' (como ocurrir\u00eda durante una inundaci\u00f3n de consultas), y ese mismo mensaje DNS es descartado seg\u00fan el l\u00edmite, hay una breve ventana de tiempo mientras la validaci\u00f3n de SIG(0) puede intentar leer el mensaje DNS ahora descartado.\nEste problema afecta a las versiones de BIND 9 9.20.0 a 9.20.22, 9.21.0 a 9.21.21, y 9.20.9-S1 a 9.20.22-S1.\nLas versiones de BIND 9 9.18.28 a 9.18.49 y 9.18.28-S1 a 9.18.49-S1 NO est\u00e1n afectadas."}], "lastModified": "2026-08-24T13:19:13.360", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*", "vulnerable": true, "matchCriteriaId": "D92461F1-BA01-479E-B740-38855CC216E6", "versionEndExcluding": "9.20.23", "versionStartIncluding": "9.20.0"}, {"criteria": "cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*", "vulnerable": true, "matchCriteriaId": "B254E8E7-3F57-4552-ACBF-623FA481B697", "versionEndExcluding": "9.21.22", "versionStartIncluding": "9.21.0"}], "operator": "OR"}]}], "sourceIdentifier": "security-officer@isc.org"}