CVE-2020-24377
📋 TL;DR
CVE-2020-24377 is a DNS rebinding vulnerability in Freebox Server web interfaces that allows attackers to bypass same-origin policy restrictions and interact with the local network interface as if they were on the local network. This affects Freebox Server devices running Freebox OS versions before 4.2.3. Attackers can exploit this to perform unauthorized actions on the device's web interface.
💻 Affected Systems
- Freebox Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of Freebox Server allowing attackers to reconfigure network settings, intercept traffic, install malicious firmware, or pivot to other devices on the local network.
Likely Case
Unauthorized access to Freebox Server web interface leading to configuration changes, DNS manipulation, or exposure of network information.
If Mitigated
Limited impact with proper network segmentation and firewall rules preventing external access to Freebox web interface.
🎯 Exploit Status
Exploitation requires DNS rebinding technique which involves controlling a malicious domain and tricking the browser into making requests to the local Freebox interface.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Freebox OS 4.2.3 and later
Vendor Advisory: https://dev.freebox.fr/blog/?p=10222
Restart Required: Yes
Instructions:
1. Log into Freebox Server web interface
2. Navigate to System Settings
3. Check for updates
4. Apply Freebox OS 4.2.3 or later update
5. Reboot the Freebox Server after update completes
🔧 Temporary Workarounds
Disable external web interface access
allConfigure firewall to block external access to Freebox Server web interface ports (typically 80/443)
Implement DNS filtering
allBlock known malicious domains and implement DNS security controls to prevent DNS rebinding attacks
🧯 If You Can't Patch
- Isolate Freebox Server on separate VLAN with strict firewall rules
- Implement network-based intrusion detection to monitor for DNS rebinding attempts
🔍 How to Verify
Check if Vulnerable:
Check Freebox OS version in web interface under System Settings > AboutCheck Version:
Not applicable - version check through web interface onlyVerify Fix Applied:
Confirm Freebox OS version is 4.2.3 or higher in System Settings > About📡 Detection & Monitoring
Log Indicators:
- Unusual DNS queries for short TTL domains
- Multiple authentication attempts from external IPs to Freebox web interface
- Configuration changes from unexpected sources
Network Indicators:
- DNS queries with very short TTL values
- HTTP requests to Freebox interface from external IPs
- Unusual port 80/443 traffic to Freebox Server
SIEM Query:
source_ip=EXTERNAL AND dest_ip=FREEBOX_IP AND (dest_port=80 OR dest_port=443) AND http_user_agent CONTAINS browser