CVE-2021-27963
📋 TL;DR
CVE-2021-27963 is an authentication bypass vulnerability in SonLogger that allows unauthenticated attackers to create new user accounts with administrative privileges. This affects SonLogger versions before 6.4.1. Attackers can exploit this to gain complete control over the application.
💻 Affected Systems
- SonLogger
📦 What is this software?
Sonlogger by Sfcyazilim
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain SuperAdmin access, enabling complete system compromise, data theft, and potential lateral movement to connected systems.
Likely Case
Unauthenticated attackers create administrative accounts to access sensitive logging data and modify system configurations.
If Mitigated
With proper network segmentation and authentication controls, impact is limited to the SonLogger instance only.
🎯 Exploit Status
Exploitation requires only curl or similar HTTP client to send POST request to /User/saveUser endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.4.1
Vendor Advisory: https://www.sonlogger.com/releasenotes
Restart Required: Yes
Instructions:
1. Download SonLogger 6.4.1 or later from official vendor site. 2. Backup current configuration and data. 3. Install the updated version. 4. Restart the SonLogger service. 5. Verify authentication is required for user creation.
🔧 Temporary Workarounds
Network Access Control
allRestrict network access to SonLogger web interface using firewall rules
# Example iptables rule: iptables -A INPUT -p tcp --dport [SonLogger_port] -s [trusted_network] -j ACCEPT
# Windows Firewall: New-NetFirewallRule -DisplayName "Block SonLogger" -Direction Inbound -Protocol TCP -LocalPort [SonLogger_port] -Action Block
Web Application Firewall
allBlock POST requests to /User/saveUser endpoint from unauthenticated sources
# ModSecurity rule: SecRule REQUEST_METHOD "@streq POST" "chain,id:1001,phase:2,deny,status:403,msg:'Block SonLogger exploit'"
SecRule REQUEST_URI "@beginsWith /User/saveUser" "chain"
SecRule REMOTE_USER "^$"
🧯 If You Can't Patch
- Implement strict network segmentation to isolate SonLogger from untrusted networks
- Deploy a reverse proxy with authentication requirements for all /User/ endpoints
🔍 How to Verify
Check if Vulnerable:
Attempt to send POST request to http://[sonlogger_host]/User/saveUser with user creation payload without authentication. If successful, system is vulnerable.Check Version:
Check SonLogger web interface login page or about section for version numberVerify Fix Applied:
Attempt same POST request after patching - should receive authentication error or 403 response.📡 Detection & Monitoring
Log Indicators:
- POST requests to /User/saveUser from unauthenticated sources
- New user creation events without corresponding authentication logs
- Multiple failed authentication attempts followed by successful user creation
Network Indicators:
- HTTP POST to /User/saveUser endpoint with user creation parameters
- Traffic from unexpected sources to SonLogger web interface
SIEM Query:
source="sonlogger.log" AND (uri_path="/User/saveUser" AND http_method="POST") AND NOT (user!="anonymous")