CVE-2026-5947

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 breakdown

Affected products

• isc / bind9.20.0 – 9.20.23
• isc / BIND 99.20.0 – 9.20.22
• isc / BIND 99.21.0 – 9.21.21
• isc / BIND 99.20.9-S1 – 9.20.22-S1
• isc / BIND 99.18.28 – 9.18.49
• isc / BIND 99.18.28-S1 – 9.18.49-S1

References

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