CVE-2024-39249: Async Library ReDoS Vulnerability

CVE-2024-39249 Overview

CVE-2024-39249 is a Regular Expression Denial of Service (ReDoS) vulnerability affecting the Async JavaScript library, a popular utility module for working with asynchronous JavaScript. The vulnerability exists in the autoinject function's parsing logic, where a regular expression pattern can be exploited to cause catastrophic backtracking when processing specially crafted input.

Critical Impact

Applications using vulnerable versions of Async may experience significant performance degradation or complete service unavailability when the autoInject function processes malicious input strings, leading to denial of service conditions.

Note: This vulnerability is disputed by the supplier, who argues there is no realistic threat model since regular expressions are not used with untrusted input in typical usage scenarios.

Affected Products

• Async <= 2.6.4 (2.x branch)
• Async <= 3.2.5 (3.x branch)

Discovery Timeline

• 2024-07-01 - CVE CVE-2024-39249 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-39249

Vulnerability Analysis

The vulnerability stems from an inefficient regular expression pattern used within the autoInject.js module of the Async library. When the function parses function parameters to determine dependency injection requirements, it utilizes a regex that exhibits exponential time complexity under certain input conditions. This creates an opportunity for ReDoS attacks where an attacker can provide carefully constructed strings that trigger excessive backtracking in the regex engine, consuming CPU resources and potentially blocking the Node.js event loop.

The weakness is classified under CWE-1333 (Inefficient Regular Expression Complexity), which describes scenarios where regular expressions are implemented in ways that allow adversaries to consume excessive system resources through algorithmic complexity attacks.

Root Cause

The root cause lies in the regular expression implementation within the autoInject function's parameter parsing logic. The regex pattern contains nested quantifiers or alternation structures that create pathological backtracking scenarios when matched against adversarial input strings. Specifically, the vulnerable code is located in the autoInject.js module where function signatures are parsed.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker who can influence the input processed by the autoInject function could supply specially crafted strings designed to maximize regex backtracking. However, the supplier disputes the practical exploitability of this vulnerability, noting that in typical usage patterns, the regular expressions do not process untrusted input.

The vulnerability mechanism works as follows: when the regex engine encounters a malicious input string, it enters a state of catastrophic backtracking where the number of steps grows exponentially with input length. This can cause the Node.js event loop to become blocked, resulting in denial of service for the entire application.

Detection Methods for CVE-2024-39249

Indicators of Compromise

• Abnormal CPU utilization spikes in Node.js processes, particularly in applications using Async library
• Event loop blocking or significant latency increases in application response times
• Application hangs or timeouts when processing specific function injection patterns
• Monitoring alerts indicating thread or process starvation in affected services

Detection Strategies

• Implement application performance monitoring (APM) to detect unusual CPU consumption patterns in Node.js runtimes
• Monitor for blocked event loop indicators using Node.js diagnostic tools such as blocked-at or similar profiling libraries
• Scan dependencies using software composition analysis (SCA) tools to identify vulnerable Async library versions
• Review application logs for timeout errors or unresponsive behavior correlated with autoInject function usage

Monitoring Recommendations

• Configure alerting thresholds for Node.js process CPU usage exceeding baseline metrics
• Implement event loop lag monitoring with tools like prom-client for Prometheus integration
• Set up dependency vulnerability scanning in CI/CD pipelines to flag affected Async versions
• Monitor application response time percentiles for anomalies indicating potential ReDoS exploitation

How to Mitigate CVE-2024-39249

Immediate Actions Required

• Audit your application's package dependencies to identify usage of Async versions <= 2.6.4 or <= 3.2.5
• Evaluate whether your application passes untrusted input to the autoInject function and assess actual risk
• Review the GitHub Issue discussion for vendor guidance on the disputed nature of this vulnerability
• Consider the supplier's position that this is not exploitable in realistic scenarios before implementing changes

Patch Information

As of the last modification date, the vendor disputes this vulnerability and indicates that the regular expression is not designed to process untrusted input. Organizations should monitor the Async GitHub repository for any future updates or patches. Review the CVE-2024-39249 repository and the related issue discussion for additional technical context.

Workarounds

• Ensure that only trusted, validated input is passed to the autoInject function in your application code
• Implement input validation and length restrictions before data reaches the Async library functions
• Consider using alternative dependency injection patterns that do not rely on regex-based function parsing
• Apply timeout mechanisms around potentially vulnerable function calls to prevent complete service unavailability

# Check for vulnerable Async versions in your Node.js project
npm list async
npm audit

# If using yarn
yarn list --pattern async
yarn audit