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CVE-2026-55203

9.0 critical SSVC exploitation: none Analyzed
NVD · CVE.org

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.

Fix

Patch, vendor advisory and mitigation references on NVD 1

Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.

Change history 1

  1. First seenCVSS 9.0 · haproxyNVD modified 2026-10-08 17:12

Affected (CPE criteria) 1

  • cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*

References 2