CVE-2025-29953: Critical Deserialization of Untrusted Data Vulnerability in Apache ActiveMQ NMS OpenWire Client

Overview

This blog post aims to shed light on a critical cybersecurity vulnerability, CVE-2025-29953, which affects the Apache ActiveMQ NMS OpenWire Client before version 2.1.1. This vulnerability revolves around the deserialization of untrusted data when connecting to untrusted servers, which can potentially allow malicious servers to execute arbitrary code on the client. Such attacks could potentially compromise the system or lead to data leakage. It’s essential for users, particularly those using Apache ActiveMQ NMS OpenWire Client, to understand this vulnerability and take the necessary steps to protect their systems.

Vulnerability Summary

CVE ID: CVE-2025-29953
Severity: Critical (9.8 CVSS Score)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: System compromise or data leakage

Affected Products

Product | Affected Versions

Apache ActiveMQ NMS OpenWire Client | Before 2.1.1

How the Exploit Works

This vulnerability stems from the unbounded deserialization that occurs when the Apache ActiveMQ NMS OpenWire Client tries to establish connections with untrusted servers. The servers can manipulate this flaw by providing malicious responses that will eventually lead to arbitrary code execution on the client. Although version 2.1.0 introduced a feature to restrict deserialization through allow/denylist, this feature could be bypassed, leaving the client vulnerable.

Conceptual Example Code

The following pseudocode illustrates how this vulnerability might be exploited:

// Server-side code simulating a malicious server
public class MaliciousServer {
public static void main(String[] args) throws Exception {
ServerSocket serverSocket = new ServerSocket(8000);
Socket clientSocket = serverSocket.accept();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(clientSocket.getOutputStream());
objectOutputStream.writeObject(new MaliciousObject());
}
static class MaliciousObject implements Serializable {
private void readObject(ObjectInputStream in) throws Exception {
Runtime.getRuntime().exec("malicious_command");
}
}
}

In this example, a malicious server is set up to send a serialized malicious object to the client. When the client deserializes the object, the malicious command within the object’s readObject method is executed.

How to Mitigate the Vulnerability

Users are advised to upgrade to Apache ActiveMQ NMS OpenWire Client version 2.1.1, which rectifies the issue. In addition to this, it is recommended to move away from relying on .NET binary serialization as a future hardening method, given the deprecation of the built-in .NET binary serialization feature from .NET 9 onwards. As a temporary mitigation, users can apply a vendor patch or use a Web Application Firewall (WAF) or Intrusion Detection System (IDS).