CVE-2026-55203

Name of the Vulnerable Software and Affected Versions HAProxy versions prior to 3.4.0

Description An integer overflow exists in the drl field of the fcgi conn structure within the FastCGI parser. When the contentLength is 65535 and the paddingLength is 1 or more, the drl field wraps to 0. This causes the system to misparse FastCGI record headers and desynchronize the framing state machine. A malicious or spoofed FastCGI backend can exploit this to corrupt request and response boundaries, leading to request routing errors, response smuggling across clients, or memory safety issues.

Recommendations Apply commit 5985276 to resolve the issue in versions prior to 3.4.0.