Dashboard / CVE-2026-55203

CVE-2026-55203

CRITICAL
INFO Priority: 0.03 BB Relevance: 78/100
Published: 2026-06-18 Modified: 2026-10-26 First seen: 2026-10-29 Status: active

Attack Surface

Network Low Complexity No Auth No Interaction Integ. Impact

CVSS Vector Breakdown

AV: Network
AC: Low
PR: None
UI: None
S: X
AT: Present
VC: None
VI: High
VA: None

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.

Weakness Classification (1)

Affected Software (6)

VendorProductVersion
haproxy haproxy < 2.4.36
haproxy haproxy 2.5 – 2.6.30
haproxy haproxy 2.7 – 2.8.25
haproxy haproxy 2.9 – 3.0.24
haproxy haproxy 3.1 – 3.2.20
haproxy haproxy 3.3 – 3.4.1

References & Advisories (2)

Bug Bounty Relevance

78 / 100
✓ Network accessible
✓ No authentication
✓ Low complexity
✓ No user interaction

CVSS Score

9.0 / 10.0 v4.0
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

EPSS — Exploitation Probability

0.33%
Raw Score 0.003340
Percentile 26.8%
Date 2026-10-29

EPSS Trend

2026-10-29
0.00334
2026-10-28
0.00334

Intelligence Sources

nvd ref →

External Links