CVE-2026-52203: MCMS Information Disclosure Vulnerability

CVE-2026-52203 Overview

CVE-2026-52203 is an information disclosure vulnerability in MCMS v6.1.1. A remote, unauthenticated attacker can obtain sensitive information by manipulating the source parameter. The weakness is classified under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor). The flaw is exploitable over the network without user interaction or prior authentication, making it accessible to any actor that can reach the affected MCMS instance.

Critical Impact
Remote unauthenticated attackers can extract sensitive information from MCMS v6.1.1 through crafted requests to the source parameter, exposing confidential application data.

Affected Products

MCMS v6.1.1

Discovery Timeline

2026-07-17 - CVE-2026-52203 published to NVD
2026-07-23 - Last updated in NVD database

Technical Details for CVE-2026-52203

Vulnerability Analysis

CVE-2026-52203 affects MCMS v6.1.1 and enables unauthorized information disclosure. The application accepts a source parameter from remote clients without sufficient access control or output filtering. An attacker can supply crafted values to retrieve information the application should not expose to unauthenticated users.

The issue maps to [CWE-200], which covers cases where an application exposes sensitive data to actors who should not have access to it. The confidentiality impact is high, while integrity and availability are not affected. This aligns with a pure disclosure primitive rather than data modification or service disruption.

The EPSS probability is 0.303% with a percentile of 22.564, indicating limited observed exploitation activity at the time of publication. Public proof-of-concept material is referenced in a GitHub Gist Vulnerability PoC.

Root Cause

The root cause is improper handling of the source parameter within MCMS v6.1.1. The parameter is trusted without validation or authorization checks, allowing it to reference or return protected resources. The application returns sensitive content in the HTTP response instead of rejecting the request.

Attack Vector

The attack vector is network-based. An attacker sends an HTTP request to a vulnerable MCMS endpoint with a manipulated source parameter value. No authentication, privileges, or user interaction are required. Successful exploitation returns sensitive data in the server response. Refer to the referenced GitHub Gist Vulnerability PoC for technical reproduction details.

Detection Methods for CVE-2026-52203

Indicators of Compromise

Unusual HTTP GET or POST requests to MCMS endpoints containing unexpected values in the source parameter.
Anomalous response sizes returned from MCMS endpoints when the source parameter is present.
Repeated parameter fuzzing patterns from a single source IP targeting MCMS URLs.

Detection Strategies

Deploy web application firewall (WAF) rules that inspect the source parameter for path traversal sequences, file extensions, or reference identifiers not used by legitimate clients.
Correlate access logs to identify unauthenticated sessions issuing requests that return unusually large or sensitive payloads.
Baseline legitimate source parameter values from application traffic and alert on deviations.

Monitoring Recommendations

Enable verbose HTTP access logging on the MCMS front-end and forward logs to a centralized analytics platform.
Monitor for spikes in 200 OK responses paired with atypical query strings targeting MCMS.
Track outbound egress volumes from the MCMS host to identify potential bulk data extraction.

How to Mitigate CVE-2026-52203

Immediate Actions Required

Restrict network access to MCMS v6.1.1 instances so they are not exposed to untrusted networks or the public internet.
Audit application logs for prior requests containing suspicious source parameter values and assess potential data exposure.
Contact the MCMS vendor for an official patched release addressing CVE-2026-52203.

Patch Information

No vendor advisory or patch URL is listed in the CVE record at the time of publication. Administrators should monitor MCMS project channels for a fixed version superseding v6.1.1 and apply it once available.

Workarounds

Implement WAF filtering to block or sanitize requests containing unexpected source parameter values.
Enforce authentication in front of MCMS using a reverse proxy where feasible.
Disable or restrict endpoints that consume the source parameter until a vendor fix is available.

bash

# Example WAF rule (ModSecurity syntax) to block suspicious source parameter values
SecRule ARGS:source "@rx (\.\./|/etc/|\.php$|\.xml$|\.conf$)" \
    "id:1052203,phase:2,deny,status:403,log,\
    msg:'CVE-2026-52203 - Suspicious MCMS source parameter'"