Name: CVE-2026-55203: Integer Overflow or Wraparound
Creator: Rapid7
Published: 2026-06-18T00:00:00.000Z
License: https://www.rapid7.com/legal/website-terms-of-use/
Keywords: CVE, CVE-2026-55203, CWE-190, CVSS 9.1, EPSS 0.00334

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.

CVSS Details

CVSS 4.0 Base Score: 9 (CRITICAL)
CVSS 4.0 Vector: (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X)
CVSS 3.1 Base Score: 9.1
CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H)

Covered by Rapid7

Product	Vendor Advisory	Solution File	Added	Published
Alma_linux	—	Upgrade haproxy	Oct 11, 2026	Aug 17, 2026
Oracle_linux	—	Upgrade haproxy	Oct 22, 2026	Jun 18, 2026
Redhat_linux	—	Upgrade haproxy-debugsourceUpgrade haproxyNo solution existsUpgrade haproxy-debuginfo	Jul 20, 2026	Jun 18, 2026
Rocky_linux	—	Upgrade haproxy-debugsourceUpgrade haproxyUpgrade haproxy-debuginfo	Aug 20, 2026	Aug 18, 2026
Ubuntu	—	Upgrade haproxy	Jun 23, 2026	Jun 22, 2026

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CVSS Details

Covered by Rapid7

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