CVE-2025-57349: Openjsf Messageformat RCE Vulnerability

CVE-2025-57349 Overview

The messageformat package, an implementation of the Unicode MessageFormat 2 specification for JavaScript, is vulnerable to prototype pollution due to improper handling of message key paths in versions prior to 2.3.0. The flaw arises when processing nested message keys containing special characters (e.g., __proto__), which can lead to unintended modification of the JavaScript Object prototype. This vulnerability may allow a remote attacker to inject properties into the global object prototype via specially crafted message input, potentially causing denial of service or other undefined behaviors in applications using the affected component.

Critical Impact

Remote attackers can exploit prototype pollution to inject malicious properties into JavaScript's Object prototype, potentially causing denial of service or enabling further attacks in applications that depend on the messageformat package.

Affected Products

• openjsf messageformat (versions prior to 2.3.0)

Discovery Timeline

• 2025-09-24 - CVE CVE-2025-57349 published to NVD
• 2025-10-17 - Last updated in NVD database

Technical Details for CVE-2025-57349

Vulnerability Analysis

This vulnerability is classified as Prototype Pollution (CWE-1321), a class of security flaw specific to JavaScript applications. The messageformat package fails to properly sanitize nested message key paths during processing, allowing attackers to inject special property names like __proto__, constructor, or prototype into the object hierarchy.

When an application processes user-controlled message input through the vulnerable messageformat library, an attacker can craft input containing malicious key paths that traverse to and modify the base Object prototype. Since all JavaScript objects inherit from Object.prototype, any properties added to it become accessible on all objects within the application context.

The attack is network-accessible and requires no authentication or user interaction, making it particularly dangerous for web applications that process untrusted message formatting input.

Root Cause

The root cause lies in the improper handling of message key paths within the messageformat package. When the library processes nested keys, it does not validate or sanitize key names to prevent access to prototype chain properties. This allows specially crafted keys containing __proto__ or similar dangerous property names to traverse the prototype chain and modify Object.prototype, affecting all objects in the JavaScript runtime.

Attack Vector

The attack is executed remotely over the network by supplying malicious message input to an application using the vulnerable messageformat package. An attacker crafts a message with nested keys designed to exploit the prototype pollution vulnerability. When processed, these keys navigate the prototype chain and inject attacker-controlled properties into Object.prototype.

The exploitation requires:

1. An application using messageformat versions prior to 2.3.0
2. User-controllable input that gets processed by the messageformat library
3. Crafted message keys containing prototype-accessing property names

For technical details on the vulnerability mechanism and discussion, see the GitHub Issue Discussion.

Detection Methods for CVE-2025-57349

Indicators of Compromise

• Unexpected properties appearing on JavaScript objects that were not explicitly defined
• Application crashes or undefined behavior related to object property access
• Error logs indicating unexpected object prototype modifications
• Anomalous input patterns containing __proto__, constructor.prototype, or similar strings in message formatting requests

Detection Strategies

• Implement input validation to detect and block message keys containing __proto__, constructor, or prototype strings
• Deploy Web Application Firewall (WAF) rules to filter requests containing prototype pollution payloads
• Use runtime application self-protection (RASP) solutions to monitor for prototype modifications
• Scan application dependencies using software composition analysis (SCA) tools to identify vulnerable messageformat versions

Monitoring Recommendations

• Monitor application logs for unusual error patterns related to object property access or type errors
• Implement logging for all message formatting operations to capture potentially malicious input
• Set up alerts for dependency vulnerability scanners when vulnerable package versions are detected
• Track JavaScript runtime exceptions that may indicate prototype pollution exploitation attempts

How to Mitigate CVE-2025-57349

Immediate Actions Required

• Upgrade the messageformat package to version 2.3.0 or later immediately
• Audit applications using messageformat to identify exposure to untrusted input
• Implement input validation to sanitize message keys before processing
• Review application code for any patterns that pass user-controlled data to messageformat functions

Patch Information

The vulnerability is addressed in messageformat version 2.3.0 and later. Organizations should update their package dependencies to the patched version. For additional context and patch details, refer to the GitHub Issue Discussion.

Workarounds

• Implement a sanitization layer that strips or rejects message keys containing __proto__, constructor, or prototype before passing data to messageformat
• Use Object.freeze(Object.prototype) to prevent modifications to the Object prototype (note: this may break legitimate application functionality)
• Employ object creation with Object.create(null) for sensitive data structures to avoid prototype chain inheritance
• Restrict messageformat processing to trusted, validated input sources only until patching is complete

# Upgrade messageformat to patched version
npm update messageformat@^2.3.0

# Verify installed version
npm list messageformat

# For yarn users
yarn upgrade messageformat@^2.3.0