---
id: CVE-2026-55203
title: >-
  HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow
  vulnerability in the fcgi_conn structure's drl field that allows buffer
  misparse as new FCGI record headers
summary: >-
  HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow
  vulnerability in the fcgi_conn structure's drl field that allows buffer
  misparse as new FCGI record headers. When contentLength is 65535 and
  paddingLength is 1 …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N'
cwe:
  - CWE-190
vendor: haproxy
product: haproxy
affected:
  - haproxy < 2.4.36
  - 'haproxy >= 2.5, < 2.6.30'
  - 'haproxy >= 2.7, < 2.8.25'
  - 'haproxy >= 2.9, < 3.0.24'
  - 'haproxy >= 3.1, < 3.2.20'
  - 'haproxy >= 3.3, < 3.4.1'
patched:
  - haproxy 3.4.1
published: '2026-06-18'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T17:12:58.233'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55203'
references:
  - url: >-
      https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field
    label: disclosure@vulncheck.com
tags:
  - nvd
epss: 0.00576
epssPercentile: 0.45751
ingestedAt: '2026-10-08T17:56:11.697Z'
---

## Overview

HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer misparse as new FCGI record headers. When contentLength is 65535 and paddingLength is 1 or more, the drl field wraps to 0, causing incorrect record consumption and allowing malicious FastCGI backends to desynchronize the FCGI framing parser, potentially causing request routing errors, response smuggling, or memory safety issues.

## Affected

- `haproxy < 2.4.36`
- `haproxy >= 2.5, < 2.6.30`
- `haproxy >= 2.7, < 2.8.25`
- `haproxy >= 2.9, < 3.0.24`
- `haproxy >= 3.1, < 3.2.20`
- `haproxy >= 3.3, < 3.4.1`

## Remediation

Upgrade past the affected range:

- `haproxy 3.4.1`