CVE-2026-31272: MRCMS Auth Bypass Vulnerability

CVE-2026-31272 Overview

CVE-2026-31272 is a critical broken access control vulnerability in MRCMS version 3.1.2, a Java-based content management system. The vulnerability exists in the save() method within src/main/java/org/marker/mushroom/controller/UserController.java, which fails to implement proper authorization validation. This security flaw allows unauthenticated remote attackers to directly create super administrator accounts, effectively bypassing all authentication mechanisms and gaining complete control over the affected CMS installation.

Critical Impact

Unauthenticated attackers can create super administrator accounts without any authentication, leading to complete system compromise and unauthorized administrative access.

Affected Products

• MRCMS 3.1.2

Discovery Timeline

• 2026-04-07 - CVE-2026-31272 published to NVD
• 2026-04-09 - Last updated in NVD database

Technical Details for CVE-2026-31272

Vulnerability Analysis

This vulnerability falls under CWE-284 (Improper Access Control), representing a fundamental failure in the application's security architecture. The affected save() method in the UserController.java class processes user creation requests without verifying whether the requesting entity has appropriate privileges to perform such sensitive operations. This architectural flaw means the endpoint responsible for creating user accounts, including those with elevated privileges, is exposed to any network-accessible client.

The vulnerability enables complete administrative takeover because attackers can craft requests that directly invoke the user creation functionality with super administrator privileges. Once an attacker creates a privileged account, they gain full control over the CMS, including the ability to modify content, access sensitive data, install malicious plugins, and potentially pivot to attack the underlying server infrastructure.

Root Cause

The root cause of this vulnerability is the absence of authentication and authorization checks in the save() method of the UserController class. The method processes incoming requests to create user accounts but fails to verify:

1. Whether the requester is authenticated
2. Whether the requester has administrative privileges to create new users
3. Whether the requester is authorized to assign super administrator roles

This oversight allows any unauthenticated user to send requests to the user creation endpoint and successfully create accounts with arbitrary privilege levels.

Attack Vector

The attack can be executed remotely over the network without any prior authentication or user interaction. An attacker identifies a vulnerable MRCMS installation and sends a crafted HTTP request to the user creation endpoint. The request includes parameters specifying super administrator privileges for the new account. Due to the missing authorization checks, the application processes the request and creates the privileged account.

The attacker then authenticates using the newly created super administrator credentials, gaining full administrative access to the MRCMS installation. This access can be leveraged for data theft, defacement, malware distribution, or as a pivot point for further attacks on the network infrastructure.

For detailed technical information about this vulnerability, refer to the vulnerability disclosure report on GitHub.

Detection Methods for CVE-2026-31272

Indicators of Compromise

• Unexpected user accounts with super administrator privileges appearing in the system
• HTTP requests to user creation endpoints from unauthenticated sessions or unexpected IP addresses
• Unusual administrative activity or configuration changes from newly created accounts
• Access logs showing requests to /UserController/save or similar endpoints without prior authentication

Detection Strategies

• Monitor web server access logs for POST requests to user management endpoints without associated authentication tokens
• Implement alerts for new administrator account creation, especially when the creating session lacks proper authentication
• Deploy web application firewalls (WAF) with rules to detect and block unauthenticated requests to sensitive administrative endpoints
• Review user accounts regularly to identify unauthorized administrator-level accounts

Monitoring Recommendations

• Enable detailed logging for all user management operations including account creation, modification, and privilege changes
• Configure SIEM rules to correlate authentication failures with subsequent successful administrative actions
• Monitor for lateral movement following any suspicious account creation activity
• Implement real-time alerting for any new account granted super administrator privileges

How to Mitigate CVE-2026-31272

Immediate Actions Required

• Restrict network access to the MRCMS administrative interface to trusted IP addresses only
• Audit all existing user accounts and remove any unauthorized super administrator accounts
• Place the application behind a reverse proxy with authentication requirements
• Monitor for any signs of exploitation including unauthorized account creation or suspicious administrative activity

Patch Information

No official vendor patch has been confirmed at the time of publication. Organizations should monitor the MRCMS project for security updates and apply any patches immediately when available. Consult the vulnerability disclosure on GitHub for the latest information.

Workarounds

• Implement network-level access controls to restrict access to the MRCMS application from untrusted networks
• Deploy a web application firewall (WAF) to filter requests to user management endpoints
• Temporarily disable the user creation functionality if feasible for your environment
• Consider implementing custom authentication middleware in front of the application until an official patch is released

# Example: Restrict access to MRCMS admin endpoints using iptables
# Allow only trusted admin IP to access the application
iptables -A INPUT -p tcp --dport 8080 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP