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.
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
| 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 | Sep 16, 2026 |
| libunbound8 · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | libunbound8 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| libunbound8 · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | libunbound8 1.13.1-1ubuntu5.17 | Sep 16, 2026 |
| libunbound8 · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | libunbound8 1.19.2-1ubuntu3.12 | Sep 16, 2026 |
| libunbound8 · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | libunbound8 1.24.2-1ubuntu2.4 | Sep 16, 2026 |
| python-unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | python-unbound 1.6.7-1ubuntu2.6+esm6 | Sep 16, 2026 |
| python-unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | python-unbound 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| python3-unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | python3-unbound 1.6.7-1ubuntu2.6+esm6 | Sep 16, 2026 |
| python3-unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | python3-unbound 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| python3-unbound · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | python3-unbound 1.13.1-1ubuntu5.17 | Sep 16, 2026 |
| python3-unbound · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | python3-unbound 1.19.2-1ubuntu3.12 | Sep 16, 2026 |
| python3-unbound · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | python3-unbound 1.24.2-1ubuntu2.4 | Sep 16, 2026 |
| unbound · Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | DEBIAN-CVE-2026-40691 | Jul 28, 2026 |
| unbound · Debian 14 | 1.25.2-1 | DEBIAN-CVE-2026-40691 | Jul 28, 2026 |
| unbound · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | unbound 1.6.7-1ubuntu2.6+esm6 | Sep 16, 2026 |
| unbound · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | unbound 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| unbound · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | unbound 1.13.1-1ubuntu5.17 | Sep 16, 2026 |
| unbound · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | unbound 1.19.2-1ubuntu3.12 | Sep 16, 2026 |
| unbound · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | unbound 1.24.2-1ubuntu2.4 | Sep 16, 2026 |
| unbound · opensuse-leap 16.0 | 1.25.2-160000.1.1 | OPENSUSE-SU-2026:21550-1 | Aug 10, 2026 |
| unbound · sles 15.6 | 1.25.2-150600.23.19.1 | SUSE-SU-2026:3885-1 | Aug 31, 2026 |
| unbound · sles 15.7 | 1.25.2-150600.23.19.1 | SUSE-SU-2026:3885-1 | Aug 31, 2026 |
| unbound · sles 16.0 | 1.25.2-160000.1.1 | SUSE-SU-2026:23226-1 | Aug 10, 2026 |
| unbound-anchor · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | unbound-anchor 1.6.7-1ubuntu2.6+esm6 | Sep 16, 2026 |
| unbound-anchor · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | unbound-anchor 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| unbound-anchor · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | unbound-anchor 1.13.1-1ubuntu5.17 | Sep 16, 2026 |
| unbound-anchor · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | unbound-anchor 1.19.2-1ubuntu3.12 | Sep 16, 2026 |
| unbound-anchor · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | unbound-anchor 1.24.2-1ubuntu2.4 | Sep 16, 2026 |
| unbound-host · Ubuntu 18.04.6 LTS (bionic) | 1.6.7-1ubuntu2.6+esm6 | unbound-host 1.6.7-1ubuntu2.6+esm6 | Sep 16, 2026 |
| unbound-host · Ubuntu 20.04 LTS (focal) | 1.9.4-2ubuntu1.11+esm3 | unbound-host 1.9.4-2ubuntu1.11+esm3 | Sep 16, 2026 |
| unbound-host · Ubuntu 22.04.1 LTS (jammy) | 1.13.1-1ubuntu5.17 | unbound-host 1.13.1-1ubuntu5.17 | Sep 16, 2026 |
| unbound-host · Ubuntu 24.04.5 LTS (noble) | 1.19.2-1ubuntu3.12 | unbound-host 1.19.2-1ubuntu3.12 | Sep 16, 2026 |
| unbound-host · Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | unbound-host 1.24.2-1ubuntu2.4 | Sep 16, 2026 |
Patch Radar data is free to use with attribution. Terms and how to credit it.
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.