Vulnerability details

CVE-2026-5947

ISC BIND 9

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

CVSS 3.1

7.5High

Official 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.

CVSS scores

Score	Version	Source	Vector
7.5High	3.1	CVEProject cvelistV5 (CNA) (isc)	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`
7.5High	3.1	CVEProject cvelistV5 (CNA) (redhat-SADP)	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`

Affected products

Vendor	Product	Versions	Source
ISC	BIND 9	9.20.0 ≤ v ≤ 9.20.22	CVEProject cvelistV5 (CNA)
ISC	BIND 9	9.20.9-S1 ≤ v ≤ 9.20.22-S1	CVEProject cvelistV5 (CNA)
ISC	BIND 9	9.21.0 ≤ v ≤ 9.21.21	CVEProject cvelistV5 (CNA)

References and advisories

https://kb.isc.org/docs/cve-2026-5947 vendor-advisory
https://downloads.isc.org/isc/bind9/9.20.23 patch
https://downloads.isc.org/isc/bind9/9.21.22 patch
https://access.redhat.com/security/cve/CVE-2026-5947 vdb-entryx_refsource_REDHAT
https://bugzilla.redhat.com/show_bug.cgi?id=2479772 issue-trackingx_refsource_REDHAT
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json x_sadp-csaf-vex
https://access.redhat.com/errata/RHSA-2026:7412 vendor-advisoryx_refsource_REDHAT

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Details

Published: 2026-05-20
Last updated: 2026-09-01
State: Published
Assigner (CNA): isc

Exploit prediction (EPSS)

1.38%

Probability of exploitation in 30 days

72.4%

Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable: Yes
Exploitation: None
Technical impact: Partial

Weaknesses (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