Race Condition Vulnerability in BIND 9 by ISC
CVE-2026-5947

7.5HIGH

Key Information:

Vendor

Isc
Status
Bind 9
Vendor
CVE Published:
20 May 2026

Badges

👾 Exploit Exists

What is CVE-2026-5947?

A race condition in BIND 9 may lead to undefined behavior through a use-after-free violation when processing DNS messages signed with SIG(0). During the validation of the signature, if the 'recursive-clients' limit is hit, the corresponding DNS message can be discarded, leaving a window in which the validation process may erroneously reference memory from the now-discarded message. This vulnerability affects specific versions of BIND 9, highlighting the importance of updating to the latest secure versions to mitigate potential exploitation risks.

Affected Version(s)

BIND 9 9.20.0 <= 9.20.22

BIND 9 9.21.0 <= 9.21.21

BIND 9 9.20.9-S1 <= 9.20.22-S1

References

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

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

ISC would like to thank Naoki Wakamatsu for bringing this vulnerability to our attention.
.