Medium severity · published May 20, 2026
CVE-2026-5947
SIG(0) validation during query flood may lead to undefined behavior
5.9
CVSS
1.4%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.4% · higher than 72% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
B9
BIND 9 · ISC
9.20.0 through 9.20.22; 9.21.0 through 9.21.21; 9.20.9-S1 through 9.20.22-S1 · source: vendor
BI
Bind · Isc
9.20.0 before 9.20.23; 9.21.0 before 9.21.22 · source: NVD
RH
Red Hat Hardened Images · Red Hat
All versions, or not specified · source: CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-5947
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-5947
Patch
https://downloads.isc.org/isc/bind9/9.20.23
Patch
https://downloads.isc.org/isc/bind9/9.21.22
Vendor Advisory
https://kb.isc.org/docs/cve-2026-5947
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:7412
access.redhat.com
https://access.redhat.com/security/cve/CVE-2026-5947
bugzilla.redhat.com
https://bugzilla.redhat.com/show_bug.cgi?id=2479772
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