CVE-2020-23776
📋 TL;DR
This is a Server-Side Request Forgery (SSRF) vulnerability in Winmail 6.5 that allows attackers to manipulate the server into making unauthorized HTTP requests to internal or external systems. Attackers can exploit this by modifying the HOST header when HTTPS is enabled. Organizations running Winmail 6.5 with HTTPS enabled are affected.
💻 Affected Systems
- Winmail
📦 What is this software?
Winmail by Winmail Project
⚠️ Risk & Real-World Impact
Worst Case
Attacker could access internal services, exfiltrate sensitive data, or pivot to other systems within the network.
Likely Case
Information disclosure from internal services, potential credential theft from metadata services, or scanning of internal network resources.
If Mitigated
Limited to unsuccessful connection attempts or access to non-sensitive endpoints if proper network segmentation and input validation are in place.
🎯 Exploit Status
Simple HTTP request manipulation required. No authentication needed. Public GitHub issue demonstrates the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
No official patch available. Consider upgrading to a newer version if available or implementing workarounds.
🔧 Temporary Workarounds
Disable HTTPS
allTemporarily disable HTTPS to mitigate the vulnerability since it only affects HTTPS configurations
Modify web server configuration to disable HTTPS/SSL
Input Validation Filter
allAdd input validation to reject malicious key parameter values
Edit app.php to validate and sanitize the key parameter before processing
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Winmail server from internal resources
- Deploy web application firewall (WAF) with SSRF protection rules
🔍 How to Verify
Check if Vulnerable:
Test by sending a request to app.php with manipulated key parameter and HOST header while HTTPS is enabledCheck Version:
Check Winmail version in admin interface or configuration filesVerify Fix Applied:
Verify that manipulated requests no longer result in server making external requests📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from Winmail server
- Requests to internal IP addresses from Winmail
- Multiple failed connection attempts to unusual domains
Network Indicators:
- Winmail server making unexpected HTTP requests to internal services
- Outbound connections to unusual ports from Winmail server
SIEM Query:
source="winmail" AND (dest_ip IN internal_ranges OR dest_port!=443)