CVE-2025-3807: Zhenfeng13 My-bbs RCE Vulnerability

CVE-2025-3807 Overview

A critical unrestricted file upload vulnerability has been identified in zhenfeng13 My-BBS version 1.0, a Java-based bulletin board system. This vulnerability affects the Upload function within the UploadController.java file located at src/main/java/com/my/bbs/controller/common/. The flaw allows remote attackers to upload arbitrary files to the server without proper validation or restrictions, potentially leading to remote code execution.

Critical Impact

Remote attackers can exploit the unrestricted file upload vulnerability to upload malicious files, including web shells or executable scripts, enabling full server compromise and unauthorized access to the underlying system.

Affected Products

• zhenfeng13 My-BBS version 1.0
• My-BBS Endpoint component (UploadController.java)
• Java-based BBS deployments using the vulnerable Upload function

Discovery Timeline

• 2025-04-19 - CVE-2025-3807 published to NVD
• 2025-10-15 - Last updated in NVD database

Technical Details for CVE-2025-3807

Vulnerability Analysis

The vulnerability resides in the file upload functionality of the My-BBS application, specifically within the Upload function of the UploadController.java component. The application fails to implement proper access control mechanisms (CWE-284: Improper Access Control) when handling file uploads through its Endpoint component.

When users submit files through the upload interface, the application does not adequately validate the file type, content, or extension before storing the file on the server. This lack of restriction allows attackers to bypass intended security controls and upload files that should be rejected, such as executable scripts, web shells, or other malicious content.

The network-accessible nature of the vulnerability means that any authenticated user with access to the upload functionality can exploit this flaw remotely. The exploit has been publicly disclosed and documented, increasing the risk of widespread exploitation.

Root Cause

The root cause of CVE-2025-3807 is improper access control implementation in the file upload handler. The Upload function in UploadController.java lacks essential security controls including:

• File type validation based on content (magic bytes)
• Whitelist-based file extension filtering
• Content-type verification
• File size limitations
• Secure file storage practices that prevent execution

This permissive upload handling allows any file type to be uploaded and potentially executed by the web server, creating a direct path to remote code execution.

Attack Vector

The attack is initiated remotely over the network. An attacker with low-privilege access to the My-BBS application can craft a malicious request to the upload endpoint. By uploading a specially crafted file—such as a JSP web shell or malicious Java class file—the attacker can achieve arbitrary code execution on the server.

The attack flow typically involves:

1. Authenticating to the My-BBS application with minimal credentials
2. Navigating to the file upload functionality
3. Uploading a malicious file (e.g., JSP shell) disguised or as-is
4. Accessing the uploaded file via its predictable URL path
5. Executing commands through the uploaded web shell

Technical details and proof-of-concept information are available in the GitHub PoC Repository and through VulDB #305661.

Detection Methods for CVE-2025-3807

Indicators of Compromise

• Unexpected files appearing in upload directories with executable extensions (.jsp, .jspx, .war, .class)
• Web server logs showing access to newly created files in upload paths immediately after upload requests
• Outbound network connections originating from the web server process
• Suspicious POST requests to /upload or similar endpoints with unusual file payloads

Detection Strategies

• Monitor file system activity in the My-BBS upload directories for creation of executable file types
• Implement web application firewall (WAF) rules to detect and block file upload attempts containing executable content
• Review HTTP access logs for sequential upload and access patterns indicative of web shell deployment
• Deploy endpoint detection and response (EDR) solutions to identify process spawning from web server contexts

Monitoring Recommendations

• Enable detailed logging for the UploadController endpoint to capture all file upload attempts with metadata
• Configure file integrity monitoring (FIM) on upload directories to alert on new or modified executable files
• Set up network monitoring to detect unusual outbound connections from the My-BBS server
• Implement real-time alerting for requests containing common web shell signatures or obfuscation patterns

How to Mitigate CVE-2025-3807

Immediate Actions Required

• Disable or restrict access to the file upload functionality until a patch is applied
• Implement strict whitelist-based file extension validation (allow only known safe types like images)
• Add content-type verification based on file magic bytes, not just headers
• Configure upload directories with non-executable permissions
• Deploy WAF rules to block suspicious file upload attempts

Patch Information

No official vendor patch is currently available for this vulnerability. Organizations using My-BBS 1.0 should implement the workarounds listed below and monitor the zhenfeng13 My-BBS repository for security updates. Consider migrating to alternative forum software with better security maintenance if no patch is forthcoming.

Workarounds

• Restrict upload functionality to trusted administrator accounts only
• Implement server-side file validation that checks both file extension and MIME type against a strict whitelist
• Store uploaded files outside the web root directory to prevent direct execution
• Rename uploaded files with random, non-guessable names and remove executable extensions
• Apply principle of least privilege to the web server user account running My-BBS

# Configuration example - Restrict upload directory execution in Apache
<Directory "/var/www/mybbs/uploads">
    # Disable script execution in upload directory
    Options -ExecCGI -Indexes
    AllowOverride None
    
    # Deny access to potentially dangerous file types
    <FilesMatch "\.(jsp|jspx|war|class|php|cgi|pl|py|sh|exe)$">
        Require all denied
    </FilesMatch>
</Directory>