CVE-2023-38327
📋 TL;DR
This CVE describes a user enumeration vulnerability in eGroupWare's calendar/freebusy.php endpoint. Unauthenticated remote attackers can determine valid usernames by analyzing server response differences. This affects eGroupWare installations with the vulnerable version exposed to untrusted networks.
💻 Affected Systems
- eGroupWare
📦 What is this software?
Egroupware by Egroupware
⚠️ Risk & Real-World Impact
Worst Case
Attackers build a complete user directory for targeted phishing, brute force attacks, or social engineering campaigns against the organization.
Likely Case
Attackers enumerate some valid usernames to improve credential stuffing or targeted phishing success rates.
If Mitigated
Limited information disclosure with no direct system compromise if proper authentication and monitoring are in place.
🎯 Exploit Status
Simple HTTP requests to calendar/freebusy.php with different usernames reveal existence based on response differences.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check eGroupWare updates after 17.1.20190111
Vendor Advisory: https://www.gruppotim.it/it/footer/red-team.html
Restart Required: No
Instructions:
1. Update eGroupWare to latest version. 2. Apply any security patches from vendor. 3. Verify calendar/freebusy.php endpoint behavior.
🔧 Temporary Workarounds
Restrict calendar/freebusy.php access
allBlock or restrict access to vulnerable endpoint using web server configuration
# Apache: <Location /calendar/freebusy.php> Require all denied </Location>
# Nginx: location ~ /calendar/freebusy\.php$ { deny all; }
Implement rate limiting
allLimit requests to calendar endpoints to prevent automated enumeration
# Use mod_evasive (Apache) or ngx_http_limit_req_module (Nginx)
🧯 If You Can't Patch
- Place eGroupWare behind authentication proxy or VPN
- Implement WAF rules to detect and block user enumeration patterns
🔍 How to Verify
Check if Vulnerable:
Send requests to /calendar/freebusy.php with valid and invalid usernames, compare response times or error messagesCheck Version:
Check eGroupWare version in admin interface or read VERSION file in installation directoryVerify Fix Applied:
Test that calendar/freebusy.php returns consistent responses regardless of username validity📡 Detection & Monitoring
Log Indicators:
- Multiple rapid requests to calendar/freebusy.php with different usernames
- Unusual pattern of 200/404 responses from calendar endpoint
Network Indicators:
- HTTP traffic to calendar/freebusy.php with username parameters
- Burst of requests from single IP to vulnerable endpoint
SIEM Query:
source="web_server" AND uri="/calendar/freebusy.php" | stats count by src_ip, user_agent