CVE-2020-35851
📋 TL;DR
CVE-2020-35851 is a command injection vulnerability in HGiga MailSherlock email security appliances. Attackers can exploit improper parameter validation to execute arbitrary system commands remotely. Organizations using vulnerable MailSherlock versions are affected.
💻 Affected Systems
- HGiga MailSherlock
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise allowing attackers to install malware, exfiltrate data, pivot to internal networks, or disrupt email security operations.
Likely Case
Attackers gain shell access to the appliance, potentially compromising email security, stealing credentials, or using the system as a foothold for further attacks.
If Mitigated
Limited impact with proper network segmentation, but still risks appliance compromise and potential email security bypass.
🎯 Exploit Status
Command injection vulnerabilities are typically easy to exploit once the vulnerable parameter is identified. The references suggest remote exploitation without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not specified in references, but vendor likely released fixed version.
Vendor Advisory: https://www.twcert.org.tw/en/cp-139-4264-f10f4-2.html
Restart Required: Yes
Instructions:
1. Contact HGiga support for the latest patched version. 2. Backup configuration. 3. Apply vendor-provided patch or upgrade to fixed version. 4. Restart appliance. 5. Verify fix.
🔧 Temporary Workarounds
Network Access Restriction
allRestrict access to MailSherlock management interface to trusted IP addresses only.
Configure firewall rules to allow only specific source IPs to access MailSherlock web/management ports.
Input Validation Enhancement
allImplement additional input validation at network perimeter if appliance supports custom rules.
Check if MailSherlock supports custom input validation rules via web interface configuration.
🧯 If You Can't Patch
- Isolate MailSherlock appliance in a dedicated network segment with strict firewall rules limiting inbound/outbound connections.
- Implement network-based intrusion prevention systems (IPS) to detect and block command injection attempts targeting the appliance.
🔍 How to Verify
Check if Vulnerable:
Check MailSherlock version against vendor advisory. If running unpatched version, assume vulnerable.Check Version:
Check via MailSherlock web interface under System Information or use vendor-specific CLI command if available.Verify Fix Applied:
Verify appliance is running patched version from vendor and test parameter validation functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual command execution patterns in system logs
- Multiple failed parameter validation attempts
- Suspicious user-agent or input strings in web logs
Network Indicators:
- Unexpected outbound connections from MailSherlock appliance
- Traffic patterns suggesting command execution (e.g., shell connections)
SIEM Query:
Example: 'source="mail-sherlock-logs" AND (command="*sh*" OR command="*cmd*" OR command="*exec*")'