CVE-2026-55203
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk24th percentile - higher than 24% of all known CVEs
Summary
HAProxy up to version 3.4.0 contains an integer overflow vulnerability in the fcgi_conn structure's drl field. When contentLength is 65535 and paddingLength is 1 or more, the drl field wraps to 0, causing incorrect buffer parsing as new FCGI record headers. This allows malicious FastCGI backends to desynchronize the FCGI framing parser.
Risk Assessment
The risk includes request routing errors, response smuggling, and potential memory safety issues, which could lead to data integrity breaches and service availability problems.
Recommendation
It is recommended to immediately update HAProxy to a version containing commit 5985276 or later, which fixes this vulnerability.
Original NVD description (English source)
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.