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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
High
Difficult to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
None
No data modification
Availability
High
Complete denial of service
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products 2
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Isc Bind
cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
|
9.20.0
|
9.20.23
|
|
Isc Bind
cpe:2.3:a:isc:bind:*:*:*:*:-:*:*:*
|
9.21.0
|
9.21.22
|
References 7
https://downloads.isc.org/isc/bind9/9.20.23
security-officer@isc.org
https://downloads.isc.org/isc/bind9/9.21.22
security-officer@isc.org
https://kb.isc.org/docs/cve-2026-5947
security-officer@isc.org
https://access.redhat.com/errata/RHSA-2026:7412
0b0ca135-0b70-47e7-9f44-1890c2a1c46c
https://access.redhat.com/security/cve/CVE-2026-5947
0b0ca135-0b70-47e7-9f44-1890c2a1c46c
https://bugzilla.redhat.com/show_bug.cgi?id=2479772
0b0ca135-0b70-47e7-9f44-1890c2a1c46c
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json
0b0ca135-0b70-47e7-9f44-1890c2a1c46c