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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| ISC | BIND 9 | 9.20.0 – ≤ 9.20.22, 9.21.0 – ≤ 9.21.21, 9.20.9-S1 – ≤ 9.20.22-S1 | 9.18.28 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | bind9 | 1:9.20.23-1 | — |
| Debian 13 | bind9 | 1:9.20.23-1~deb13u1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | bind9 | 1:9.20.18-1ubuntu2.1 | — |
| Ubuntu 25.10 | bind9 | 1:9.20.11-1ubuntu2.4 | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | bind +6 | 9.18.48-1.1.hum1 | RHSA-2026:7412 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | bind | 9.20.23-150700.3.25.1 | SUSE-SU-2026:2673-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | bind | 9.20.23-160000.1.1 | SUSE-SU-2026:22198-1 |
| SLES 16.0 | bind | 9.20.23-160000.1.1 | SUSE-SU-2026:22198-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | bind | 9.20.23-1.1 | openSUSE-SU-2026:10874-1 |
| openSUSE Leap 16.0 | bind | 9.20.23-160000.1.1 | openSUSE-SU-2026:21123-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | bind | 9.20.23-r0 | — |
| Alpine v3.23 | bind | 9.20.23-r0 | — |
| Alpine v3.22 | bind | 9.20.23-r0 | — |
| Alpine v3.21 | bind | 9.18.49-r0 | — |
| Alpine v3.20 | bind | 9.18.49-r0 | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | bind | 9.20.23-1 | — |
Advisories 6
- WID-SEC-2026-1626 Internet Systems Consortium BIND: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 10, 2026
- RHSA-2026:7412 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 10, 2026
- SUSE-SU-2026:2673-1 Security update for bind SUSE / openSUSE Security Updates · Jul 3, 2026
- openSUSE-SU-2026:21123-1 Security update for bind SUSE / openSUSE Security Updates · Jun 30, 2026
- SUSE-SU-2026:22198-1 Security update for bind SUSE / openSUSE Security Updates · Jun 24, 2026
- openSUSE-SU-2026:10874-1 bind-9.20.23-1.1 on GA media SUSE / openSUSE Security Updates · May 29, 2026
References
- CVE-2026-5947 vendor-advisory
- https://downloads.isc.org/isc/bind9/9.20.23 patch
- https://downloads.isc.org/isc/bind9/9.21.22 patch