CVE-2026-55203

Publication date 19 June 2026

Last updated 25 June 2026

Ubuntu priority

Cvss 3 Severity Score

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
haproxy	26.04 LTS resolute	Fixed 3.2.9-1ubuntu2.2
	25.10 questing	Fixed 3.0.12-0ubuntu0.25.10.5
	24.04 LTS noble	Fixed 2.8.16-0ubuntu0.24.04.3
	22.04 LTS jammy	Fixed 2.4.30-0ubuntu0.22.04.2
	20.04 LTS focal	Needs evaluation
	18.04 LTS bionic	Needs evaluation
	16.04 LTS xenial	Needs evaluation

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
haproxy	Upstream: 5985276

Severity score breakdown

CVSS version:

Base score 9.0 · Critical

Base metrics

Parameter	Value
Attack vector	Network
Attack complexity	Low
Attack requirements	Present
Privileges required	None
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

Scores

Parameter	Value
Base score	9.0 · Critical
Base + Threat score	-
Base + Environmental score	-
Base + Threat + Environmental score	-

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

Base score 7.5 · High