Patch Commitpatch
https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd CVE-2026-55203
CRITICAL
HAProxy - Integer Overflow in FCGI Demux Record Length Field
Record summary
CVE-2026-55203 has a selected CVSS score of 9.0 (critical).
Description
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.
Description source: CVE List
Exploitation context
CISA SSVC decision
ExploitationNone
AutomatableNo
Technical impactPartial
CISA Coordinator · SSVC 2.0.3 · Evaluated Jun 23, 2026 · Source: CVE List
Affected products and versions
1| Product | Source | Version range | Status |
|---|---|---|---|
haproxyBrowse haproxy / haproxyDefault status: unaffected | CVE List | Through 3.4.0 | affected |
| 5985276735777634d8c85f1d73bb7764aab0d6dd | unaffected |
References
3nvd.nist.gov
https://nvd.nist.gov/vuln/detail/CVE-2026-55203 vulncheck.comThird-party advisory
https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field