# CVE-2026-40691: Packet of death for DNSCrypt over TCP CVE-2026-40691 is fixed in 7 products on 1 platform, first by DEBIAN-CVE-2026-40691, released July 28, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-40691 - Priority: High - CVSS: 7.5 (Moderate) - EPSS: 0.0029 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 22, 2026 - Weakness: Heap-based Buffer Overflow - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40691 ## Description In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | libunbound2 Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [libunbound2 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libunbound2-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [libunbound8 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libunbound8-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [libunbound8 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libunbound8-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [libunbound8 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libunbound8-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | libunbound8 Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [libunbound8 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libunbound8-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | python-unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [python-unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-python-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | python-unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [python-unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-python-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [python3-unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-python3-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [python3-unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-python3-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [python3-unbound 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-python3-unbound-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [python3-unbound 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-python3-unbound-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | python3-unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [python3-unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-python3-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-40691](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40691.md) | Jul 28, 2026 | | Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-40691](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40691.md) | Jul 28, 2026 | | Linux | unbound Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound opensuse-leap 16.0 | 1.25.2-160000.1.1 | [OPENSUSE-SU-2026:21550-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21550-1.md) | Aug 10, 2026 | | Linux | unbound sles 15.6 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 2026 | | Linux | unbound sles 15.7 | 1.25.2-150600.23.19.1 | [SUSE-SU-2026:3885-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-3885-1.md) | Aug 31, 2026 | | Linux | unbound sles 16.0 | 1.25.2-160000.1.1 | [SUSE-SU-2026:23226-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23226-1.md) | Aug 10, 2026 | | Linux | unbound-anchor Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound-anchor 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-anchor-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound-anchor 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-anchor-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound-anchor 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-anchor-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound-anchor 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-anchor-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound-anchor Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-anchor 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-anchor-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | [unbound-host 1.6.7-1ubuntu2.6+esm6](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-unbound-host-1.6.7-1ubuntu2.6-esm6.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | [unbound-host 1.9.4-2ubuntu1.11+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-focal-unbound-host-1.9.4-2ubuntu1.11-esm3.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | [unbound-host 1.13.1-1ubuntu5.17](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-unbound-host-1.13.1-1ubuntu5.17.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | [unbound-host 1.19.2-1ubuntu3.12](https://patchblox.com/security/data/fix/linux/ubuntu-noble-unbound-host-1.19.2-1ubuntu3.12.md) | Sep 16, 2026 | | Linux | unbound-host Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-host 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-host-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 | --- Data as of 2026-11-08T13:06:02Z UTC. 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