SIG(0) validation during query flood may lead to undefined behavior

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Summary

CVECVE-2026-5947
StatePUBLISHED
Assignerisc
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-20 13:16:40 UTC
Updated2026-05-21 15:24:32 UTC
DescriptionUndefined 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.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

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

EPSS: 0.000440000 probability, percentile 0.135710000 (date 2026-05-27)

Problem Types: CWE-362 | CWE-416 | CWE-362 CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') | CWE-416 CWE-416 Use After Free

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

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

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

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 9.20.22 custom Not specified
CNA ISC BIND 9 affected 9.21.0 9.21.21 custom Not specified
CNA ISC BIND 9 affected 9.20.9-S1 9.20.22-S1 custom Not specified
CNA ISC BIND 9 unaffected 9.18.28 9.18.49 custom Not specified
CNA ISC BIND 9 unaffected 9.18.28-S1 9.18.49-S1 custom Not specified

References

ReferenceSourceLinkTags
downloads.isc.org/isc/bind9/9.21.22 [email protected] downloads.isc.org Patch
kb.isc.org/docs/cve-2026-5947 [email protected] kb.isc.org Vendor Advisory
downloads.isc.org/isc/bind9/9.20.23 [email protected] downloads.isc.org Patch
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 Naoki Wakamatsu 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: 9.20.23, 9.21.22, or 9.20.23-S1.

Workarounds

CNA: No workarounds known.

Exploits

CNA: We are not aware of any active exploits.

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