Use After Free in Isc Bind
CVE-2026-5947
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.
Vulnerability class: Race Condition
EPSS: 0.014 (70.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Isc Bind
- Isc Bind 9 — versions 9.20.0, 9.21.0, 9.20.9-S1
Weakness classification (CWE)
References
- security-officer@isc.org (Patch, patch)
- security-officer@isc.org (Patch, patch)
- CVE-2026-5947 (vendor-advisory, Vendor Advisory)
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
- 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
Frequently asked questions
- What is CVE-2026-5947?
- CVE-2026-5947 is a high-severity vulnerability in Isc Bind, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 7.5/10. Published 2026-05-20.
- How severe is CVE-2026-5947?
- High severity. CVSS v3 base score is 7.5 out of 10.