CVE-2020-7753: Trim Package ReDoS Vulnerability

CVE-2020-7753 Overview

All versions of the trim npm package are vulnerable to Regular Expression Denial of Service (ReDoS) via the trim() function. This vulnerability allows remote attackers to cause a denial of service condition by providing specially crafted input strings that trigger catastrophic backtracking in the vulnerable regular expression pattern.

Critical Impact

This ReDoS vulnerability can cause application hangs and service unavailability when processing malicious input, affecting any Node.js application that depends on the trim package for string processing operations.

Affected Products

• trim_project trim (all versions)
• Applications using the trim npm package
• Apache Airflow (as indicated by commit threads addressing this vulnerability)

Discovery Timeline

• October 27, 2020 - CVE-2020-7753 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-7753

Vulnerability Analysis

This vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption) and manifests as a Regular Expression Denial of Service (ReDoS) attack. The vulnerable code resides in the trim() function implementation, which uses a regular expression pattern susceptible to catastrophic backtracking when processing certain input strings.

ReDoS vulnerabilities occur when a regular expression contains patterns with overlapping alternatives or nested quantifiers. When malicious input is provided, the regex engine enters an exponential time complexity state, causing the application to hang while attempting to evaluate all possible matching paths. This can effectively render the application unresponsive, impacting availability.

The attack can be executed remotely over the network without requiring authentication or user interaction. The vulnerability specifically affects application availability without compromising data confidentiality or integrity.

Root Cause

The root cause of this vulnerability lies in the regular expression implementation within the trim package's core function. The regex pattern used for trimming whitespace characters contains constructs that allow for excessive backtracking when confronted with carefully crafted input strings. The vulnerable pattern fails to efficiently handle edge cases involving repeated or nested whitespace-like characters, leading to exponential time complexity during pattern matching.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can craft a malicious string containing specific character sequences that exploit the vulnerable regular expression pattern. When this input is passed to the trim() function, the regex engine enters a pathological state characterized by exponential time complexity, consuming excessive CPU resources and causing the application to become unresponsive.

The attack is particularly concerning for web applications that process user-supplied input through the trim function, as any publicly accessible endpoint accepting string data could be a potential attack surface.

Detection Methods for CVE-2020-7753

Indicators of Compromise

• Abnormally high CPU utilization on servers running Node.js applications
• Application threads becoming unresponsive or timing out during string processing operations
• Increased response times for endpoints that process user-supplied text input
• Memory consumption spikes associated with pending regex operations

Detection Strategies

• Implement dependency scanning tools to identify the vulnerable trim package in your package.json and package-lock.json files
• Monitor application performance metrics for sudden CPU spikes correlated with string processing operations
• Use static analysis tools to identify usage patterns of the trim() function with user-controlled input
• Deploy runtime application self-protection (RASP) solutions to detect ReDoS attack patterns

Monitoring Recommendations

• Configure alerting for abnormal CPU consumption patterns in Node.js application servers
• Implement request timeout monitoring to detect endpoints experiencing degraded performance
• Set up log analysis to identify repeated requests with suspicious input patterns targeting string processing endpoints
• Monitor dependency audit reports from npm for security advisories related to the trim package

How to Mitigate CVE-2020-7753

Immediate Actions Required

• Audit your Node.js applications for dependencies on the trim package using npm audit or npm ls trim
• Replace the vulnerable trim package with native JavaScript String.prototype.trim() method where possible
• Implement input length validation to limit the size of strings processed by the vulnerable function
• Consider migrating to alternative trimming libraries that do not use vulnerable regex patterns

Patch Information

As all versions of the trim package are affected by this vulnerability, the recommended approach is to remove the dependency entirely and use the native JavaScript String.prototype.trim() method, which has been available since ECMAScript 5 and does not suffer from ReDoS vulnerabilities. For detailed information on the vulnerable code, see the GitHub Code Snippet reference. Additional vulnerability details are available from Snyk JavaScript Vulnerability Advisory and Snyk Java Vulnerability Advisory.

Workarounds

• Replace usage of trim() from the package with the native String.prototype.trim() method
• Implement input length restrictions to prevent processing of excessively long strings
• Add request timeouts at the application layer to prevent long-running regex operations from blocking resources
• Use worker threads or process isolation for string processing to prevent ReDoS from affecting the main application thread

# Check for vulnerable trim package in your project
npm ls trim

# Audit for known vulnerabilities
npm audit

# Replace trim package usage with native method in your codebase
# Instead of: require('trim')(userInput)
# Use: userInput.trim()