CVE-2025-42999 - SAP NetWeaver Visual Composer Metadata Uploader – Untrusted Deserialization Vulnerability Explained

CVE-2025-42999 is a newly discovered vulnerability in SAP NetWeaver Visual Composer (VC). This vulnerability lets a user with upload permissions—sometimes even an internal or privileged user—upload harmful files. When these files are deserialized by the system, an attacker can potentially take over the host, steal data, or disrupt operations.

This post breaks down what the CVE-2025-42999 vulnerability is, how it works, who is at risk, and how it can be exploited. I’ll also include a code snippet, reference links to original advisories, and steps you can take to protect your SAP environment.

What is SAP NetWeaver Visual Composer Metadata Uploader?

SAP NetWeaver Visual Composer is a tool that lets users build visual web applications by uploading metadata files. Its Metadata Uploader lets authorized users import models—they can include workflows, mappings, or configuration files.

The Vulnerability

In insecure versions, the Metadata Uploader fails to strictly check or sanitize what gets uploaded and then deserialized. This is an example of an untrusted deserialization vulnerability. When the system tries to deserialize (convert from serialized data back into an object) a malicious file, dangerous code may get executed.

- CWE Reference: CWE-502: Deserialization of Untrusted Data

Why is CVE-2025-42999 Dangerous?

An attacker—if they have a privileged account (sometimes just a user with upload permissions)—can create a crafted metadata file.

Availability: Services can be stopped or made unstable.

Depending on server permissions, full remote code execution (RCE) may be possible.

Example: Simple Proof of Concept (PoC)

Here’s a simplified scenario—let’s say the backend uses Java serialization.

Malicious Java Object Creation

import java.io.*;
public class Exploit implements Serializable {
    static {
        try {
            Runtime.getRuntime().exec("touch /tmp/hacked_by_cve_2025_42999");
        } catch (Exception e) {
            // Handle error
        }
    }
}

Upload Exploit.ser via the Metadata Uploader.

3. If the system unserializes the object, it will execute the payload and create /tmp/hacked_by_cve_2025_42999 on the host.

NOTE: Actual SAP payloads are more complex; this is a simple demonstration of the risk.

References

- SAP Security Patch Day – June 2025 (official)
- SAP NetWeaver Visual Composer Documentation
- SAP Security Guidelines
- CWE-502: Deserialization of Untrusted Data

What Should You Do? (Mitigation)

- Upgrade: Apply all SAP security patches as soon as possible. Check for a fixed version in SAP's Security Patch Notes.
- Restrict Upload Privileges: Only trusted and necessary users should have upload rights in Visual Composer.
- Audit Uploads: Regularly review what gets uploaded and stored. Unusual files should be investigated.

Network Segmentation: Never expose management components directly to the internet.

- Custom Upload Validation: If possible, enforce filters that only allow whitelisted metadata formats.

Conclusion

CVE-2025-42999 is a serious “insider” threat in SAP NetWeaver Visual Composer, where users with upload access can potentially compromise the platform through untrusted deserialization. Even if only IT staff or developers can use Metadata Uploader, internal threats or stolen credentials make this a priority to fix.

Patch and audit your SAP systems regularly. In modern enterprise software, never trust uploaded files—even from trusted users.


*Stay safe! For the latest updates, always follow SAP Security Patch Day advisories and monitor your environment for unusual activity.*

Timeline

Published on: 05/13/2025 01:15:48 UTC
Last modified on: 05/16/2025 19:44:49 UTC