Highly exploitable, CVE-2026-55203 poses a critical security risk that could lead to severe breaches.
Status: Received on 18 Jun 2026, 17:16 UTC
Published on: 18 Jun 2026, 17:16 UTC
CVSS Release: version 3
disclosure@vulncheck.com
Primary
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N
CVE-2026-55203: 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.
The exploitability of CVE-2026-55203 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
CVE-2026-55203 presents a challenge to exploit due to its high attack complexity, but the absence of privilege requirements still makes it a viable target for skilled attackers. A thorough security review is advised.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-55203, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-55203, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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