Vulnerability Details CVE-2026-55203
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 17.0%
CVSS Severity
CVSS v3 Score 7.5