CVE-2020-7465
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code or cause denial of service through memory corruption in MPD's L2TP implementation. Attackers can exploit it by sending specially crafted L2TP control packets with AVP Q.931 Cause Code. Systems running vulnerable versions of MPD with L2TP enabled are affected.
💻 Affected Systems
- MPD (Multi-link PPP Daemon)
📦 What is this software?
Mpd by Mpd Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root/system privileges leading to complete system compromise, data theft, and persistent backdoor installation.
Likely Case
Denial of service causing service disruption and potential system crashes, with possible information disclosure from memory corruption.
If Mitigated
Limited impact if L2TP is disabled or proper network segmentation prevents access to vulnerable services.
🎯 Exploit Status
Exploitation requires sending crafted L2TP packets to vulnerable service. Public proof-of-concept exists in bug reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: MPD 5.9 and later
Vendor Advisory: https://sourceforge.net/p/mpd/bugs/70/
Restart Required: Yes
Instructions:
1. Download MPD 5.9 or later from official source. 2. Stop MPD service. 3. Install updated version. 4. Restart MPD service. 5. Verify version is 5.9+.
🔧 Temporary Workarounds
Disable L2TP functionality
linuxDisable L2TP in MPD configuration if not required
Edit MPD configuration file and remove or comment L2TP settings
Restart MPD: systemctl restart mpd
Network access control
linuxRestrict network access to MPD service using firewall rules
iptables -A INPUT -p udp --dport 1701 -j DROP
iptables -A INPUT -p tcp --dport 1701 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate MPD services from untrusted networks
- Deploy intrusion prevention systems (IPS) to detect and block L2TP exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check MPD version and configuration for L2TP enabled: mpd --version && grep -i l2tp /etc/mpd.confCheck Version:
mpd --versionVerify Fix Applied:
Verify MPD version is 5.9 or later: mpd --version | grep -E '5\.9|6\.'📡 Detection & Monitoring
Log Indicators:
- Unusual L2TP connection attempts
- MPD service crashes or restarts
- Memory corruption errors in system logs
Network Indicators:
- Malformed L2TP packets to port 1701
- Unexpected L2TP control packets with AVP Q.931 Cause Code
SIEM Query:
source="mpd.log" AND ("crash" OR "memory" OR "corruption") OR destination_port=1701 AND protocol="L2TP"