CVE-2020-26311
📋 TL;DR
CVE-2020-26311 is a Regular Expression Denial of Service (ReDoS) vulnerability in the useragent Node.js package. Attackers can cause denial of service by sending specially crafted user agent strings that trigger inefficient regular expression processing. All Node.js applications using this package are affected.
💻 Affected Systems
- useragent Node.js package
📦 What is this software?
Useragent by Useragent Project
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to CPU exhaustion from processing malicious user agent strings, potentially affecting all users of the application.
Likely Case
Degraded performance or temporary service disruption when attackers send crafted requests to vulnerable endpoints.
If Mitigated
Minimal impact with proper rate limiting, input validation, and monitoring in place to detect and block malicious patterns.
🎯 Exploit Status
Exploitation requires sending HTTP requests with malicious user agent strings. Proof of concept available in GitHub advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: None available
Vendor Advisory: https://github.com/3rd-Eden/useragent/issues/167
Restart Required: Yes
Instructions:
1. Monitor package repository for updates. 2. Consider alternative user agent parsing libraries. 3. Apply workarounds until patch is available.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement strict input validation on user agent strings before passing to useragent parser
// JavaScript example: if (userAgentString.length > 500) { rejectRequest(); }
Rate Limiting
allImplement rate limiting on endpoints that process user agent headers
// Use express-rate-limit or similar middleware
🧯 If You Can't Patch
- Implement WAF rules to block suspicious user agent patterns
- Deploy load balancers with request filtering capabilities
🔍 How to Verify
Check if Vulnerable:
Check package.json for useragent dependency: grep -r 'useragent' package.jsonCheck Version:
npm list useragentVerify Fix Applied:
Verify useragent package is removed or replaced with alternative library📡 Detection & Monitoring
Log Indicators:
- Unusually long user agent strings
- Multiple requests with similar user agent patterns
- High CPU usage on application servers
Network Indicators:
- HTTP requests with user agent strings containing repetitive patterns
- Abnormal request patterns from single IPs
SIEM Query:
source=web_logs user_agent=* AND (user_agent_length>500 OR user_agent MATCHES '*{2,}.*{2,}')