CVE-2021-42870
📋 TL;DR
CVE-2021-42870 is an out-of-bounds read vulnerability in ACCEL-PPP 1.12.0 that occurs when processing call_clear_request messages. This allows attackers to read memory beyond allocated buffers, potentially exposing sensitive information or causing denial of service. Systems running ACCEL-PPP 1.12.0 for PPPoE, L2TP, or PPTP services are affected.
💻 Affected Systems
- ACCEL-PPP
📦 What is this software?
Accel Ppp by Accel Ppp
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise if combined with other vulnerabilities, or sensitive memory disclosure including credentials and session data.
Likely Case
Denial of service causing PPP service crashes and network connectivity disruption for users.
If Mitigated
Limited information disclosure with no system compromise if proper memory protections and network segmentation are in place.
🎯 Exploit Status
Exploitation requires sending specially crafted call_clear_request messages to the ACCEL-PPP service. No public exploit code is available, but the vulnerability is relatively straightforward to trigger.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.13.0 and later
Vendor Advisory: https://github.com/xebd/accel-ppp/issues/158
Restart Required: Yes
Instructions:
1. Download ACCEL-PPP 1.13.0 or later from the official repository. 2. Stop the ACCEL-PPP service. 3. Install the updated version. 4. Restart the ACCEL-PPP service.
🔧 Temporary Workarounds
Network Filtering
linuxBlock call_clear_request messages at network perimeter
iptables -A INPUT -p tcp --dport 1701 -m string --string "call_clear_request" --algo bm -j DROP
iptables -A INPUT -p udp --dport 1701 -m string --string "call_clear_request" --algo bm -j DROP
🧯 If You Can't Patch
- Implement network segmentation to isolate ACCEL-PPP servers from untrusted networks
- Deploy intrusion detection systems to monitor for anomalous call_clear_request patterns
🔍 How to Verify
Check if Vulnerable:
Check ACCEL-PPP version: accel-ppp --version. If output shows 1.12.0, system is vulnerable.Check Version:
accel-ppp --versionVerify Fix Applied:
After patching, verify version shows 1.13.0 or later and test PPP connectivity remains functional.📡 Detection & Monitoring
Log Indicators:
- ACCEL-PPP crash logs
- Segmentation fault errors in system logs
- Abnormal call_clear_request processing messages
Network Indicators:
- Unusual volume of call_clear_request packets
- PPP session disruptions following specific packet patterns
SIEM Query:
source="accel-ppp.log" AND ("segmentation fault" OR "out of bounds" OR "call_clear_request")