CVE-2021-37262
📋 TL;DR
CVE-2021-37262 is a regex injection vulnerability in JFinal_cms 5.1.0 that allows attackers to craft malicious regular expressions, causing excessive CPU consumption and denial of service. This affects all systems running the vulnerable version of JFinal_cms content management system. Attackers can exploit this without authentication to crash the application.
💻 Affected Systems
- JFinal_cms
📦 What is this software?
Jfinal Cms by Jflyfox
⚠️ Risk & Real-World Impact
Worst Case
Complete application unavailability due to CPU exhaustion, potentially affecting all services on the same server.
Likely Case
Application becomes unresponsive or crashes when malicious regex patterns are processed, requiring restart.
If Mitigated
Limited impact with proper input validation and regex timeout configurations in place.
🎯 Exploit Status
Proof of concept available in GitHub issue. Simple HTTP requests with crafted regex patterns can trigger the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.1.1 or later
Vendor Advisory: https://github.com/jflyfox/jfinal_cms/issues/23
Restart Required: Yes
Instructions:
1. Download latest version from GitHub. 2. Backup current installation. 3. Replace vulnerable files with patched version. 4. Restart application server.
🔧 Temporary Workarounds
Input validation filter
allAdd regex pattern validation to filter malicious input before processing
Implement input validation in application code to reject complex regex patterns
Regex timeout configuration
allConfigure regex engine timeout limits to prevent CPU exhaustion
Set Pattern.compile() with timeout: Pattern.compile(pattern, Pattern.DOTALL).matcher(input).find()
🧯 If You Can't Patch
- Implement WAF rules to block requests containing complex regex patterns
- Rate limit requests to vulnerable endpoints and monitor for abnormal CPU usage
🔍 How to Verify
Check if Vulnerable:
Check application version in admin panel or configuration files for version 5.1.0Check Version:
Check pom.xml or application.properties for version informationVerify Fix Applied:
Verify version is 5.1.1 or later and test with known exploit patterns📡 Detection & Monitoring
Log Indicators:
- High CPU usage spikes
- Application crash logs
- Requests with unusual regex patterns in parameters
Network Indicators:
- HTTP requests with complex regex patterns in parameters
- Repeated requests to same endpoint
SIEM Query:
source="web_server" AND (url="*regex*" OR param="*regex*") AND status=500