CVE-2025-24959: zx Tool RCE Vulnerability

CVE-2025-24959 Overview

CVE-2025-24959 is a Code Injection vulnerability in Google zx, a popular tool for writing better scripts in Node.js. An attacker with control over environment variable values can inject unintended environment variables into process.env through the dotenv.stringify function. This vulnerability can lead to arbitrary command execution or unexpected behavior in applications that rely on environment variables for security-sensitive operations.

Critical Impact

Applications that process untrusted input and pass it through dotenv.stringify are particularly vulnerable to environment variable injection, which could lead to arbitrary command execution.

Affected Products

• Google zx versions prior to 8.3.2
• Applications using dotenv.stringify with untrusted input

Discovery Timeline

• 2025-02-03 - CVE-2025-24959 published to NVD
• 2025-02-03 - Last updated in NVD database

Technical Details for CVE-2025-24959

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code) and affects the dotenv.stringify function in Google zx. The root issue lies in improper input validation when processing environment variable values, allowing attackers to break out of intended variable boundaries and inject additional environment variables. When these malicious environment variables are later consumed by shell commands or child processes, they can alter application behavior or enable command execution in ways not anticipated by developers.

The attack requires local access with low privileges, though user interaction is necessary for successful exploitation. Applications that accept user-controlled input and pass it through the vulnerable function without proper sanitization are at risk of having their runtime environment manipulated.

Root Cause

The vulnerability stems from insufficient sanitization of special characters in environment variable values passed to dotenv.stringify. Specifically, the function does not properly escape or validate characters such as double quotes ("), single quotes ('), and backticks, which can be used to terminate variable assignments prematurely and inject new environment variable definitions.

Attack Vector

The attack requires local access to the target system. An attacker must craft malicious input containing special characters that break out of the expected environment variable value context. When this input is processed by dotenv.stringify and subsequently used by the application, the injected environment variables become part of process.env, potentially influencing security-sensitive operations or enabling command execution when shell commands are spawned.

The vulnerability mechanism involves exploiting improper handling of quote characters and backticks in the dotenv.stringify function. For detailed technical analysis, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-24959

Indicators of Compromise

• Unexpected or malformed environment variables appearing in process.env
• Environment variable values containing unescaped quote characters or backticks from external input
• Anomalous child process execution with unexpected environment configurations

Detection Strategies

• Monitor application logs for errors related to environment variable parsing or unexpected command execution
• Implement runtime checks to validate environment variable contents against expected patterns
• Use static code analysis tools to identify uses of dotenv.stringify with untrusted input

Monitoring Recommendations

• Audit applications using Google zx to identify instances where dotenv.stringify processes user-controlled input
• Implement input validation logging to track potentially malicious environment variable values
• Monitor for suspicious command execution patterns that may indicate successful exploitation

How to Mitigate CVE-2025-24959

Immediate Actions Required

• Upgrade Google zx to version 8.3.2 or later immediately
• Audit code for uses of dotenv.stringify with untrusted input and implement input sanitization
• Enforce strict validation of environment variable values before processing

Patch Information

The vulnerability has been patched in Google zx version 8.3.2. Users should upgrade to this version immediately to mitigate the vulnerability. The fix addresses the improper handling of special characters in environment variable values. For patch details, see the GitHub Pull Request.

Workarounds

• Sanitize user-controlled environment variable values before passing them to dotenv.stringify
• Avoid using double quotes ("), single quotes ('), and backticks in environment variable values from untrusted sources
• Implement strict allowlists for environment variable names and value patterns in security-sensitive applications

# Example validation before using dotenv.stringify
# Strip or reject values containing dangerous characters
ENV_VALUE=$(echo "$USER_INPUT" | tr -d '"\\x60')
# Validate against expected patterns before use
if [[ ! "$ENV_VALUE" =~ ^[a-zA-Z0-9_-]+$ ]]; then
    echo "Invalid environment variable value"
    exit 1
fi