CVE-2026-55203

critical · 9

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.

CVSS

0.3%

EPSS (exploit prob.)

28th

EPSS percentile

2026-06-18

Published

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Weaknesses

CWE-190

Affected products

Vendor	Product	Affected versions
haproxy	haproxy	<= 3.4.0

Check a specific version with /api/v1/cve/match.

References

https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd
https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field

Query this programmatically:

curl https://evil-db.io/api/v1/cve/CVE-2026-55203