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CVE-2026-55203 Details

Description

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.

Metrics

CVSS 3.x Severity and Vector Strings:

NIST: [email protected]CVSS-B:9.1 CRITICALVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CNA: [email protected]CVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd	[email protected]	Patch
https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-190	Integer Overflow or Wraparound	[email protected]

Affected Products

Product	Versions
haproxy haproxy	<= 3.4.0
CPE cpe:2.3:a:haproxy:haproxy:::::::: Remediation No remediation found in references.

Change History

4 change records found show changes

Date	Action	Recorded By
Jul 14, 2026	CVE Modified	[email protected]
Jun 26, 2026	Initial Analysis	[email protected]
Jun 23, 2026	CVE Modified	CISA-ADP
Jun 18, 2026	New CVE Received	[email protected]