CVE-2021-35370
📋 TL;DR
CVE-2021-35370 is a critical vulnerability in Peacexie Imcat v5.4 that allows attackers to execute arbitrary code due to incomplete input filtering. This affects all systems running the vulnerable version of Imcat, potentially giving attackers full control over affected servers.
💻 Affected Systems
- Peacexie Imcat
📦 What is this software?
Imcat by Txjia
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal data, install malware, or pivot to other systems.
Likely Case
Remote code execution leading to web server compromise, data theft, and potential lateral movement within the network.
If Mitigated
Limited impact with proper network segmentation, WAF rules, and minimal privileges, potentially reducing to denial of service.
🎯 Exploit Status
The vulnerability is in input filtering, making exploitation relatively straightforward once the attack vector is identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v5.5 or later
Vendor Advisory: https://github.com/peacexie/imcat/issues/8
Restart Required: Yes
Instructions:
1. Backup current Imcat installation and data. 2. Download latest version from official repository. 3. Replace vulnerable files with patched version. 4. Restart web server. 5. Verify functionality.
🔧 Temporary Workarounds
Web Application Firewall Rules
allImplement WAF rules to block malicious input patterns targeting the vulnerable filtering function.
# Example ModSecurity rule: SecRule ARGS "@rx malicious_pattern" "id:1001,phase:2,deny"
Network Segmentation
linuxRestrict access to Imcat application to only necessary users and networks.
# Example iptables rule: iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
# iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Isolate the vulnerable system in a separate network segment with strict access controls.
- Implement application-level input validation and sanitization for all user inputs.
🔍 How to Verify
Check if Vulnerable:
Check Imcat version in admin panel or by examining version files. If version is exactly 5.4, system is vulnerable.Check Version:
grep -r 'version.*5\.4' /path/to/imcat/installation/ || cat /path/to/imcat/version.txtVerify Fix Applied:
After patching, verify version shows 5.5 or later and test input filtering functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to Imcat endpoints
- Suspicious command execution patterns in web server logs
- Multiple failed input validation attempts
Network Indicators:
- Unusual outbound connections from web server
- Traffic patterns matching known exploit payloads
SIEM Query:
source="web_server" AND (url="*/imcat/*" OR user_agent CONTAINS "imcat") AND (status=500 OR bytes_out>1000000)