CVE-2026-5947
SIG(0) validation during query flood may lead to undefined behavior
- Published
- Updated
- Reserved
- Assigned by
- isc
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| iscCNA (assigner) | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| redhat-SADPADP (enrichment) | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Modified | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 1.4% · top 28% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.
Weakness
- CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (opens in a new tab)All about CWE-362 and its CVEs
- CWE-416 Use After Free (opens in a new tab)All about CWE-416 and its CVEs
- CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition (opens in a new tab)All about CWE-367 and its CVEs
Affected products
What to do
Solution: Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.23, 9.21.22, or 9.20.23-S1.
Workaround: No workarounds known.
Exploitation: We are not aware of any active exploits.
References (7)
- CVE-2026-5947 (opens in a new tab)vendor-advisory
- https://downloads.isc.org/isc/bind9/9.20.23 (opens in a new tab)patch
- https://downloads.isc.org/isc/bind9/9.21.22 (opens in a new tab)patch
- https://access.redhat.com/security/cve/CVE-2026-5947 (opens in a new tab)vdb-entryx_refsource_REDHAT
- RHBZ#2479772 (opens in a new tab)issue-trackingx_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json (opens in a new tab)x_sadp-csaf-vex
- https://access.redhat.com/errata/RHSA-2026:7412 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-5947)Record last updated .