🛡️ CVE-2026-55203 — haproxy

🔴 CVSS 9.5 — Critical ✅ No Known Exploit CWE-190 OSV
9.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

HAProxy - Integer Overflow in FCGI Demux Record Length Field

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality low, integrity high, availability none.

Weakness class

CVE-2026-55203 is classified as CWE-190: Integer Overflow or Wraparound. Arithmetic produces a value too large for its type and wraps around, so a later size or bounds check passes when it should not.

Affected software

CVE-2026-55203 is recorded against 1 package.

  • haproxy

Timeline and source

Published on 29 June 2026 and last revised on 14 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Web)
www.vulncheck.com (Web)

Details

Severity CRITICAL
CVSS Score 9.5
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
CWE CWE-190
Public Exploit ✅ No
Source OSV
Published 2026-06-29
Updated 2026-08-12
Modified 2026-07-14

Affected Packages

Software From version Fixed in
haproxy — —

Similar Threats

Exploit Protection

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