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Linux Distros Unpatched Vulnerability : CVE-2026-55203

critical Nessus Plugin ID 321685

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Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - 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. (CVE-2026-55203)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

See Also

https://security-tracker.debian.org/tracker/CVE-2026-55203

https://ubuntu.com/security/CVE-2026-55203

Plugin Details

Severity: Critical

ID: 321685

File Name: unpatched_CVE_2026_55203.nasl

Version: 1.7

Type: Local

Agent: unix

Family: Misc.

Published: 6/20/2026

Updated: 7/3/2026

Supported Sensors: Agentless Assessment, Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.3

Percentile: 53.62

CVSS v2

Risk Factor: High

Base Score: 9.4

Temporal Score: 8

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:C

CVSS Score Source: CVE-2026-55203

CVSS v3

Risk Factor: Critical

Base Score: 9.1

Temporal Score: 8.3

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:U/RC:C

CVSS v4

Risk Factor: Critical

Base Score: 9

Threat Score: 6.5

Threat Vector: CVSS:4.0/E:U

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

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, cpe:/o:canonical:ubuntu_linux:20.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:haproxy, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, p-cpe:/a:debian:debian_linux:haproxy, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, cpe:/o:debian:debian_linux:12.0, cpe:/o:debian:debian_linux:13.0

Required KB Items: Host/cpu, Host/local_checks_enabled, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 6/18/2026

Reference Information

CVE: CVE-2026-55203