CVE-2021-42054
📋 TL;DR
ACCEL-PPP 1.12.0 contains an out-of-bounds read vulnerability in the triton_context_schedule function that occurs when a client disconnects after authentication. This allows attackers to potentially read sensitive memory contents or cause denial of service. Organizations running ACCEL-PPP servers 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, though this requires specific memory layout conditions
Likely Case
Denial of service causing ACCEL-PPP service crashes and disruption of PPP connections
If Mitigated
Limited information disclosure or service instability if proper memory protections are in place
🎯 Exploit Status
Exploitation requires client authentication first, then controlled disconnection. The vulnerability is in the cleanup code path after authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.13.0 and later
Vendor Advisory: https://github.com/xebd/accel-ppp/issues/156
Restart Required: Yes
Instructions:
1. Download ACCEL-PPP 1.13.0 or later from official repository. 2. Compile and install the updated version. 3. Restart ACCEL-PPP service. 4. Verify the fix by checking version.
🔧 Temporary Workarounds
Disable client authentication
linuxPrevents exploitation by removing the authentication requirement, though this reduces security
Modify ACCEL-PPP configuration to remove auth modules
Rate limit connections
linuxLimit connection attempts to reduce exploitation attempts
Configure iptables or firewall rules to limit PPP connection rates
🧯 If You Can't Patch
- Implement network segmentation to isolate ACCEL-PPP servers from untrusted networks
- Deploy memory protection mechanisms like ASLR and DEP if not already enabled
🔍 How to Verify
Check if Vulnerable:
Check ACCEL-PPP version: if running 1.12.0, the system is vulnerableCheck Version:
accel-ppp --version or check installed package versionVerify Fix Applied:
Verify ACCEL-PPP version is 1.13.0 or later and monitor for crashes after client disconnections📡 Detection & Monitoring
Log Indicators:
- ACCEL-PPP service crashes
- Segmentation fault errors in system logs
- Unexpected client disconnections after auth
Network Indicators:
- Multiple PPP authentication attempts followed by immediate disconnections
- Unusual traffic patterns to PPP ports
SIEM Query:
source="accel-ppp.log" AND ("segmentation fault" OR "crash" OR "SIGSEGV")