CVE-2020-12620
📋 TL;DR
CVE-2020-12620 is a command injection vulnerability in Pi-hole 4.4 that allows authenticated users with write access to /etc/pihole/dns-servers.conf to execute arbitrary commands with elevated privileges. This affects Pi-hole administrators and users with local access to the Pi-hole system. The vulnerability stems from improper neutralization of shell metacharacters in DNS server configuration.
💻 Affected Systems
- Pi-hole
📦 What is this software?
Pi Hole by Pi Hole
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with root privileges, allowing attacker to install malware, exfiltrate data, pivot to other systems, or disrupt DNS services.
Likely Case
Local privilege escalation leading to unauthorized configuration changes, DNS manipulation, or installation of backdoors on the Pi-hole system.
If Mitigated
Limited impact if proper file permissions restrict write access to /etc/pihole/dns-servers.conf to only trusted administrators.
🎯 Exploit Status
Exploitation requires authenticated access to modify DNS server configuration. Public proof-of-concept demonstrates command injection via DNS server IP field.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Pi-hole 4.4.1 and later
Vendor Advisory: https://github.com/pi-hole/pi-hole/releases/tag/v4.4.1
Restart Required: No
Instructions:
1. Update Pi-hole using: pihole -up
2. Verify update with: pihole -v
3. The update patches the command injection vulnerability in DNS server configuration handling.
🔧 Temporary Workarounds
Restrict file permissions
linuxChange permissions on /etc/pihole/dns-servers.conf to prevent unauthorized writes
sudo chmod 644 /etc/pihole/dns-servers.conf
sudo chown root:root /etc/pihole/dns-servers.conf
Disable DNS server configuration changes
linuxRemove write access to DNS configuration for non-admin users
sudo chmod 600 /etc/pihole/dns-servers.conf
🧯 If You Can't Patch
- Implement strict access controls to limit who can modify /etc/pihole/dns-servers.conf
- Monitor for suspicious modifications to DNS server configuration files
🔍 How to Verify
Check if Vulnerable:
Check Pi-hole version: pihole -v | grep 'Pi-hole version' - if it shows 4.4, the system is vulnerable.Check Version:
pihole -v | grep 'Pi-hole version'Verify Fix Applied:
Verify Pi-hole version is 4.4.1 or later: pihole -v | grep 'Pi-hole version'📡 Detection & Monitoring
Log Indicators:
- Unusual commands in Pi-hole logs
- Unexpected modifications to /etc/pihole/dns-servers.conf
- Suspicious DNS configuration changes
Network Indicators:
- Unexpected outbound connections from Pi-hole system
- DNS queries to unusual domains
SIEM Query:
source="pihole" AND (event="config_change" OR file_path="/etc/pihole/dns-servers.conf")