CVE-2026-5947

Summary

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.

Affected Software

Weaknesses

• CWE-362: CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
• CWE-416: CWE-416 Use After Free

Workarounds

No workarounds known.

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

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

Additional References

• https://access.redhat.com/security/cve/CVE-2026-5947
• https://bugzilla.redhat.com/show_bug.cgi?id=2479772
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json
• https://access.redhat.com/errata/RHSA-2026:7412

References

• https://kb.isc.org/docs/cve-2026-5947
• https://downloads.isc.org/isc/bind9/9.20.23
• https://downloads.isc.org/isc/bind9/9.21.22

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