# CVE-2025-40777: A possible assertion failure when 'stale-answer-client-timeout' is set to '0' CVE-2025-40777 is fixed in 20 products on 1 platform, first by bind9 1:9.20.4-3ubuntu1.2, released July 16, 2025. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2025-40777 - Priority: High - CVSS: 7.5 (Moderate) - EPSS: 0.0102 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 16, 2025 - Weakness: Reachable Assertion - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-40777 ## Description If a `named` caching resolver is configured with `serve-stale-enable``yes`, and with `stale-answer-client-timeout` set to `0` (the onlyallowable value other than `disabled`), and if the resolver, in the processof resolving a query, encounters a CNAME chain involving a specificcombination of cached or authoritative records, the daemon will abort withan assertion failure.This issue affects BIND 9 versions 9.20.0 through 9.20.10, 9.21.0 through9.21.9, and 9.20.9-S1 through 9.20.10-S1. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bind amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind sles 15.7 | 9.20.11-150700.3.6.1 | [SUSE-SU-2025:02349-1](https://patchblox.com/security/data/fix/linux/suse-su-2025-02349-1.md) | Jul 17, 2025 | | Linux | bind-chroot amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-debuginfo amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-debugsource amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-devel amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-dnssec-utils amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-dnssec-utils-debuginfo amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-doc amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-libs amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-libs-debuginfo amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-license amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-utils amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind-utils-debuginfo amzn 2023 | 32:9.18.33-1.amzn2023.0.3 | [ALAS2023-2025-1105](https://patchblox.com/security/data/fix/linux/alas2023-2025-1105.md) | Jul 21, 2025 | | Linux | bind9 Debian 13.5 (trixie) | 1:9.20.11-1 | [DEBIAN-CVE-2025-40777](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40777.md) | Jul 16, 2025 | | Linux | bind9 Debian 14 | 1:9.20.11-1 | [DEBIAN-CVE-2025-40777](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40777.md) | Jul 16, 2025 | | Linux | bind9 Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | bind9-dnsutils Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9-dnsutils 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9-dnsutils-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | bind9-host Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9-host 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9-host-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | bind9-libs Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9-libs 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9-libs-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | bind9-utils Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9-utils 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9-utils-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | bind9utils Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [bind9utils 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-bind9utils-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | | Linux | dnsutils Ubuntu 25.04 (plucky) | 1:9.20.4-3ubuntu1.2 | [dnsutils 1:9.20.4-3ubuntu1.2](https://patchblox.com/security/data/fix/linux/ubuntu-plucky-dnsutils-1-9.20.4-3ubuntu1.2.md) | Jul 16, 2025 | --- Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.