Description
If a `named` caching resolver is configured with `serve-stale-enable` `yes`, and with `stale-answer-client-timeout` set to `0` (the only allowable value other than `disabled`), and if the resolver, in the process of resolving a query, encounters a CNAME chain involving a specific combination of cached or authoritative records, the daemon will abort with an assertion failure.
This issue affects BIND 9 versions 9.20.0 through 9.20.10, 9.21.0 through 9.21.9, and 9.20.9-S1 through 9.20.10-S1.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| ISC | BIND 9 | 9.20.0 – ≤ 9.20.10, 9.21.0 – ≤ 9.21.9, 9.20.9-S1 – ≤ 9.20.10-S1 | 9.18.0 |
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 | 1:9.20.11-1 | — |
| Debian 13 | bind9 | 1:9.20.11-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 25.04 | bind9 | 1:9.20.4-3ubuntu1.2 | USN-7641-1 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | bind | 9.20.11-150700.3.6.1 | SUSE-SU-2025:02349-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | bind | 9.20.11-1.1 | openSUSE-SU-2025:15354-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | bind | 9.20.11-r0 | — |
| Alpine v3.23 | bind | 9.20.11-r0 | — |
| Alpine v3.22 | bind | 9.20.11-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | bind +7 | 32:9.18.33-1.amzn2023.0.3 | ALAS2023-2025-1105 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | bind | 9.20.15-1 | — |
Advisories 5
- openSUSE-SU-2025:15354-1 bind-9.20.11-1.1 on GA media SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2025:02349-1 Security update for bind SUSE / openSUSE Security Updates · Mar 23, 2026
- USN-7641-1 bind9 vulnerability Ubuntu Security Notices (USN) · Oct 13, 2025
- ALAS2023-2025-1105 Important: bind security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 8, 2025
- WID-SEC-2025-1585 Internet Systems Consortium BIND: Mehrere Schwachstellen BSI CERT-Bund (WID) · Jul 17, 2025
References
- CVE-2025-40777 vendor-advisory