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Threat Model Analysis for faisalman/ua-parser-js

Threat: Regular Expression Denial of Service (ReDoS) via Crafted User-Agent

1. Threat: Regular Expression Denial of Service (ReDoS) via Crafted User-Agent

  • Description: An attacker sends a specially crafted, malicious User-Agent string to the application. This string is designed to trigger catastrophic backtracking in the regular expressions used by ua-parser-js for parsing. The attacker's goal is to consume excessive CPU resources, causing the application to become slow or unresponsive, effectively creating a denial-of-service condition. The attacker might use publicly available ReDoS payloads or tools to generate these malicious strings.
  • Impact: The application becomes unavailable or severely degraded for legitimate users. Depending on the application's architecture, this could affect all users or only those whose requests are processed by the affected server instance. Prolonged attacks could lead to resource exhaustion and potentially system crashes.
  • Affected Component: The core parsing engine of ua-parser-js. Specifically, any function that processes the raw User-Agent string, including (but not limited to):
    • new UAParser(uaString): The constructor when a User-Agent string is provided.
    • UAParser.getResult(): The method that returns the parsed results.
    • Individual getter methods like getBrowser(), getOS(), getDevice(), etc., as they all rely on the initial parsing.
  • Risk Severity: Critical. This is a well-known and easily exploitable vulnerability that can directly impact application availability.
  • Mitigation Strategies:
    • Update ua-parser-js: Prioritize using the absolute latest version. This is the single most effective mitigation, as maintainers actively fix ReDoS vulnerabilities.
    • Implement Timeouts: Wrap calls to ua-parser-js functions in a timeout mechanism. If parsing exceeds a short, predefined time (e.g., 10-50 milliseconds), terminate the operation. Return a default value or an error.
    • Rate Limiting: Limit the number of requests per IP address or user session, especially those that trigger User-Agent parsing. This mitigates the impact of an attacker sending many malicious requests.
    • WAF (Web Application Firewall): Use a WAF that can detect and block known ReDoS patterns in User-Agent strings. This provides a layer of defense before the request reaches your application.
    • Input Length Restriction (Limited): Impose a reasonable maximum length on the User-Agent string before passing it to ua-parser-js. This reduces the attack surface but does not eliminate the risk. Do not rely solely on this.
    • Server-Side Monitoring: Monitor CPU usage and application response times. Alert on anomalies that might indicate a ReDoS attack.

Threat: Supply Chain Compromise of ua-parser-js

2. Threat: Supply Chain Compromise of ua-parser-js

  • Description: An attacker compromises the ua-parser-js library itself, either by gaining control of the source code repository (e.g., on GitHub), the npm registry account, or by compromising a dependency of ua-parser-js. The attacker injects malicious code into the library. When an application updates to this compromised version, the malicious code is executed.
  • Impact: Potentially very high, ranging from data exfiltration to complete system compromise. The attacker's code runs with the privileges of the application using ua-parser-js.
  • Affected Component: The entire ua-parser-js library, and potentially any code within the application that interacts with it.
  • Risk Severity: High. Although less likely than ReDoS, the potential impact is severe.
  • Mitigation Strategies:
    • Use Lockfiles: Employ package-lock.json (npm) or yarn.lock (yarn) to ensure that the exact versions of ua-parser-js and all its dependencies are installed consistently. These files contain cryptographic hashes to verify integrity.
    • Software Composition Analysis (SCA): Use SCA tools to scan your project's dependencies for known vulnerabilities and supply chain risks. These tools can alert you to compromised or outdated libraries.
    • Code Audits (High-Security Contexts): For applications with stringent security requirements, consider conducting periodic security audits of ua-parser-js and its critical dependencies.
    • Monitor Security Advisories: Stay informed about security advisories related to ua-parser-js and the npm ecosystem.