CVE-2026-55203
HAProxy - Integer Overflow in FCGI Demux Record Length Field
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-190 |
| Vendor | haproxy |
| Product | haproxy |
| Published | Jun 18, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
Low
Integrity
High
Availability
None
Affected Versions
haproxy / haproxy
0 ≤ 3.4.0
References
Credits
Tristan Madani (@TristanInSec)