SIG(0) validation during query flood may lead to undefined behavior
CVE-2026-5947 is fixed in 6 products on 1 platform, first by bind9 1:9.20.18-1ubuntu2.1, released May 19, 2026. It is not reported as exploited. Patch Radar priority: High.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| bind · opensuse-leap 16.0 | 9.20.23-160000.1.1 | OPENSUSE-SU-2026:21123-1 | Jun 20, 2026 |
| bind · sles 15.7 | 9.20.23-150700.3.25.1 | SUSE-SU-2026:2673-1 | Jul 2, 2026 |
| bind · sles 16.0 | 9.20.23-160000.1.1 | SUSE-SU-2026:22198-1 | Jun 20, 2026 |
| bind9 · Debian 13.5 (trixie) | 1:9.20.23-1~deb13u1 | DEBIAN-CVE-2026-5947 | May 27, 2026 |
| bind9 · Debian 14 | 1:9.20.23-1 | DEBIAN-CVE-2026-5947 | May 27, 2026 |
| bind9 · Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.4 | bind9 1:9.20.11-1ubuntu2.4 | May 27, 2026 |
| bind9 · Ubuntu 26.04.1 LTS (resolute) | 1:9.20.18-1ubuntu2.1 | bind9 1:9.20.18-1ubuntu2.1 | May 19, 2026 |
| bind9-dnsutils · Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.4 | bind9-dnsutils 1:9.20.11-1ubuntu2.4 | May 27, 2026 |
| bind9-dnsutils · Ubuntu 26.04.1 LTS (resolute) | 1:9.20.18-1ubuntu2.1 | bind9-dnsutils 1:9.20.18-1ubuntu2.1 | May 19, 2026 |
| bind9-host · Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.4 | bind9-host 1:9.20.11-1ubuntu2.4 | May 27, 2026 |
| bind9-host · Ubuntu 26.04.1 LTS (resolute) | 1:9.20.18-1ubuntu2.1 | bind9-host 1:9.20.18-1ubuntu2.1 | May 19, 2026 |
| bind9-libs · Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.4 | bind9-libs 1:9.20.11-1ubuntu2.4 | May 27, 2026 |
| bind9-libs · Ubuntu 26.04.1 LTS (resolute) | 1:9.20.18-1ubuntu2.1 | bind9-libs 1:9.20.18-1ubuntu2.1 | May 19, 2026 |
| bind9-utils · Ubuntu 25.10 (questing) | 1:9.20.11-1ubuntu2.4 | bind9-utils 1:9.20.11-1ubuntu2.4 | May 27, 2026 |
| bind9-utils · Ubuntu 26.04.1 LTS (resolute) | 1:9.20.18-1ubuntu2.1 | bind9-utils 1:9.20.18-1ubuntu2.1 | May 19, 2026 |
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