# CVE-2026-40209: dnsdist: An attacker might be able to cause outgoing TCP connections to backend to be stuck until a timeout occurs instead of...

CVE-2026-40209 is fixed in dnsdist on 1 platform, first by DEBIAN-CVE-2026-40209, released June 26, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-40209
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0070
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 25, 2026

## Description

An attacker might be able to cause outgoing TCP connections to backend to be stuck until a timeout occurs instead of being released immediately, by sending IXFR queries. This could be used to cause a denial of service if there is a limit to the number of concurrent connections to this backend, or if the process runs out of file descriptors.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | dnsdist Debian 13.5 (trixie) | 1.9.15-0+deb13u1 | [DEBIAN-CVE-2026-40209](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40209.md) | Jun 26, 2026 |
| Linux | dnsdist Debian 14 | 2.1.0-1 | [DEBIAN-CVE-2026-40209](https://patchblox.com/security/data/fix/linux/debian-cve-2026-40209.md) | Jun 26, 2026 |
| Linux | dnsdist opensuse-leap 16.0 | 1.9.15-160000.1.1 | [OPENSUSE-SU-2026:21533-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21533-1.md) | Aug 5, 2026 |
| Linux | dnsdist sles 16.0 | 1.9.15-160000.1.1 | [SUSE-SU-2026:23146-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23146-1.md) | Aug 5, 2026 |

---

Data as of 2026-11-08T06:59:42Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo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.