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
Updated2026-07-15 01:16:46 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-367 | CWE-362 CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') | CWE-416 CWE-416 Use After Free | CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

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
3.1ADPCVSS7.5HIGHCVSS:3.1/AV:N/AC:L/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
3.10b0ca135-0b70-47e7-9f44-1890c2a1c46cSecondary7.5HIGHCVSS: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
ADP Red Hat Red Hat Hardened Images unaffected 9.18.48-1.1.hum1 * rpm Not specified
ADP Red Hat Red Hat Enterprise Linux 10 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 6 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 7 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 8 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 8 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 9 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 9 Not specified Not specified
ADP Red Hat Red Hat Enterprise Linux 9 Not specified Not specified
ADP Red Hat Red Hat OpenShift Container Platform 4 Not specified Not specified

References

ReferenceSourceLinkTags
downloads.isc.org/isc/bind9/9.21.22 [email protected] downloads.isc.org Patch
bugzilla.redhat.com/show_bug.cgi 0b0ca135-0b70-47e7-9f44-1890c2a1c46c bugzilla.redhat.com
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
access.redhat.com/errata/RHSA-2026:7412 0b0ca135-0b70-47e7-9f44-1890c2a1c46c access.redhat.com
security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json 0b0ca135-0b70-47e7-9f44-1890c2a1c46c security.access.redhat.com
access.redhat.com/security/cve/CVE-2026-5947 0b0ca135-0b70-47e7-9f44-1890c2a1c46c access.redhat.com
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

SourceTimeEvent
ADP2026-05-19T09:59:51.277ZReported to Red Hat.
ADP2026-05-21T12:15:50.513ZMade public.

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.

ADP: RHSA-2026:7412: Red Hat Hardened Images

Workarounds

CNA: No workarounds known.

ADP: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Exploits

CNA: We are not aware of any active exploits.

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