CVE-2026-40691
Fixed in a distro release EPSS <1%CVSS 7.5
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.
Products: NLnet Labs unbound
Distro releases
| Release | Package | Fixed in |
|---|---|---|
| Debian 12 | unbound | no fix |
| Debian 13 | unbound | 1.26.1-0+deb13u1 |
| Debian 14 | unbound | 1.25.2-1 |
| Red Hat hummingbird 1 | python3-unbound | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-anchor | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-devel | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-dracut | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-libs | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-munin | 0:1.25.2-0.1.hum1 |
| Red Hat hummingbird 1 | unbound-utils | 0:1.25.2-0.1.hum1 |
| SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Micro 5.5 | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Module for Basesystem 15 SP7 | unbound | 1.25.2-150600.23.19.1 |
| SUSE Linux Enterprise Module for Package Hub 15 SP7 | unbound | 1.25.2-150600.23.19.1 |
| SUSE Linux Enterprise Server 15 SP4-LTSS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Server 15 SP5-LTSS | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Server 15 SP6-LTSS | unbound | 1.25.2-150600.23.19.1 |
| SUSE Linux Enterprise Server 16.0 | unbound | 1.25.2-160000.1.1 |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | unbound | 1.25.2-150100.10.28.1 |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | unbound | 1.25.2-150600.23.19.1 |
| SUSE Linux Enterprise Server for SAP applications 16.0 | unbound | 1.25.2-160000.1.1 |
| SUSE Linux Micro 6.0 | unbound | 1.25.2-1.1 |
| SUSE Linux Micro 6.1 | unbound | 1.25.2-slfo.1.1_1.1 |
| SUSE Linux Micro 6.2 | unbound | 1.25.2-160000.1.1 |
| Ubuntu 22.04 LTS | unbound | 1.13.1-1ubuntu5.17 |
| Ubuntu 24.04 LTS | unbound | 1.19.2-1ubuntu3.12 |
| Ubuntu 26.04 LTS | unbound | 1.24.2-1ubuntu2.4 |
| Ubuntu 26.10 | unbound | no fix |
| Ubuntu Pro 14.04 LTS | unbound | 1.4.22-1ubuntu4.14.04.3+esm5 |
| Ubuntu Pro 16.04 LTS | unbound | 1.5.8-1ubuntu1.1+esm5 |
| Ubuntu Pro 18.04 LTS | unbound | 1.6.7-1ubuntu2.6+esm6 |
| Ubuntu Pro 20.04 LTS | unbound | 1.9.4-2ubuntu1.11+esm3 |
| openSUSE Leap 16.0 | unbound | 1.25.2-160000.1.1 |
| openSUSE Tumbleweed | unbound | 1.25.2-1.1 |