CVE-2021-40901
📋 TL;DR
CVE-2021-40901 is a Regular Expression Denial of Service (ReDoS) vulnerability in scniro-validator v1.0.1 that allows attackers to cause excessive CPU consumption by submitting specially crafted invalid email addresses. This affects any application using this specific version of the scniro-validator library for email validation.
💻 Affected Systems
- scniro-validator
📦 What is this software?
Scniro Validator by Scniro Validator Project
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to CPU exhaustion, potentially affecting all users of the application.
Likely Case
Degraded performance and intermittent service disruptions for users during attack periods.
If Mitigated
Minimal impact with proper rate limiting, input validation, and monitoring in place.
🎯 Exploit Status
ReDoS vulnerabilities are relatively easy to exploit with publicly available patterns. The GitHub repository shows the vulnerable code.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.0.2 or later
Vendor Advisory: https://github.com/yetingli/SaveResults/blob/main/js/scniro-validator.js
Restart Required: Yes
Instructions:
1. Update scniro-validator to v1.0.2 or later. 2. Restart the application. 3. Verify the fix is applied.
🔧 Temporary Workarounds
Input Length Limitation
allLimit email input length before validation to prevent ReDoS patterns
// JavaScript example: if(email.length > 254) reject
Rate Limiting
allImplement rate limiting on email validation endpoints
🧯 If You Can't Patch
- Implement Web Application Firewall (WAF) rules to block suspicious email patterns
- Deploy monitoring for abnormal CPU spikes during email validation operations
🔍 How to Verify
Check if Vulnerable:
Check package.json or similar dependency files for scniro-validator version 1.0.1Check Version:
npm list scniro-validator (for Node.js applications)Verify Fix Applied:
Verify scniro-validator version is 1.0.2 or later in dependencies📡 Detection & Monitoring
Log Indicators:
- Unusually long email addresses in validation logs
- Multiple failed validation attempts from single source
Network Indicators:
- High volume of email validation requests
- Requests with unusually long email parameters
SIEM Query:
source="application_logs" AND (email_length>254 OR validation_time>5000ms)