# CVE-2026-110354: HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request. Although the H1 multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without making progress. The affected thread stays busy at 100% CPU after timeouts expire and after the client disconnects, and repeated requests can consume all worker threads until the process is restarted.

CVE-2026-110354 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-110354, released October 27, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-110354
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0081
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 21, 2026
- Weakness: Loop with Unreachable Exit Condition ('Infinite Loop')
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-110354

## Description

HAProxy 3 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (persistent worker-thread CPU exhaustion) via an HTTP/1.1 chunked request. Although the H1 multiplexer drains the request before closing the stream, the parser repeatedly re-processes the same bytes without making progress. The affected thread stays busy at 100% CPU after timeouts expire and after the client disconnects, and repeated requests can consume all worker threads until the process is restarted.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | haproxy Debian 12.15 (bookworm) | 2.6.12-1+deb12u4 | [DEBIAN-CVE-2026-110354](https://patchblox.com/security/data/fix/linux/debian-cve-2026-110354.md) | Oct 27, 2026 |
| Linux | haproxy Debian 13.5 (trixie) | 3.0.11-1+deb13u4 | [DEBIAN-CVE-2026-110354](https://patchblox.com/security/data/fix/linux/debian-cve-2026-110354.md) | Oct 27, 2026 |
| Linux | haproxy Debian 14 | 3.2.26-1 | [DEBIAN-CVE-2026-110354](https://patchblox.com/security/data/fix/linux/debian-cve-2026-110354.md) | Oct 27, 2026 |
| Linux | haproxy Ubuntu 22.04.1 LTS (jammy) | 2.4.30-0ubuntu0.22.04.3 | [haproxy 2.4.30-0ubuntu0.22.04.3](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-haproxy-2.4.30-0ubuntu0.22.04.3.md) | Nov 4, 2026 |
| Linux | haproxy Ubuntu 24.04.5 LTS (noble) | 2.8.30-0ubuntu0.24.04.2 | [haproxy 2.8.30-0ubuntu0.24.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-haproxy-2.8.30-0ubuntu0.24.04.2.md) | Nov 4, 2026 |
| Linux | haproxy Ubuntu 26.04.1 LTS (resolute) | 3.2.25-0ubuntu0.26.04.2 | [haproxy 3.2.25-0ubuntu0.26.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-haproxy-3.2.25-0ubuntu0.26.04.2.md) | Nov 7, 2026 |
| Linux | vim-haproxy Ubuntu 22.04.1 LTS (jammy) | 2.4.30-0ubuntu0.22.04.3 | [vim-haproxy 2.4.30-0ubuntu0.22.04.3](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-vim-haproxy-2.4.30-0ubuntu0.22.04.3.md) | Nov 4, 2026 |
| Linux | vim-haproxy Ubuntu 24.04.5 LTS (noble) | 2.8.30-0ubuntu0.24.04.2 | [vim-haproxy 2.8.30-0ubuntu0.24.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-vim-haproxy-2.8.30-0ubuntu0.24.04.2.md) | Nov 4, 2026 |
| Linux | vim-haproxy Ubuntu 26.04.1 LTS (resolute) | 3.2.25-0ubuntu0.26.04.2 | [vim-haproxy 3.2.25-0ubuntu0.26.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-vim-haproxy-3.2.25-0ubuntu0.26.04.2.md) | Nov 7, 2026 |

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Data as of 2026-11-09T13:31:49Z 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

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