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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements Present

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact Low

Subsequent System Integrity Impact High

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Changed

Confidentiality Impact Low

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
haproxy haproxy unaffected
Version Status Constraints
0 affected ≤ 3.4.0
5985276735777634d8c85f1d73bb7764aab0d6dd unaffected —

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Project Subscriptions

Vendors Products
Haproxy Subscribe
Aloha Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd cve-icon
https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field cve-icon
History

Thu, 18 Jun 2026 16:45:00 +0000

Type Values Removed Values Added
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.
Title HAProxy - Integer Overflow in FCGI Demux Record Length Field
First Time appeared Haproxy
Haproxy aloha
Weaknesses CWE-190
CPEs cpe:2.3:a:haproxy:aloha:*:*:*:*:*:*:*:*
Vendors & Products Haproxy
Haproxy aloha
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N'}

cvssV4_0

{'score': 9, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-06-18T16:05:20.100Z

Reserved: 2026-06-16T15:53:37.764Z

Link: CVE-2026-55203

cve-icon Vulnrichment

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cve-icon NVD

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cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses