CVE-2025-25567
📋 TL;DR
SoftEther VPN 5.02.5187 contains a buffer overflow vulnerability in the UniToStrForSingleChars function within Internat.c. This could allow arbitrary code execution, though the vendor disputes the severity, claiming it only enables local users to attack themselves through the UI. Systems running the vulnerable version are affected.
💻 Affected Systems
- SoftEther VPN
📦 What is this software?
Vpn by Softether
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker gains full system control via arbitrary code execution, potentially leading to complete system compromise and lateral movement.
Likely Case
Local authenticated user triggers buffer overflow through UI interaction, causing application crash or limited code execution in their own context.
If Mitigated
With proper network segmentation and least privilege, impact limited to individual user session disruption.
🎯 Exploit Status
Proof-of-concept available in references, but vendor disputes remote exploitability. Likely requires local access or authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch available. Monitor SoftEther VPN website for updates.
🔧 Temporary Workarounds
Restrict Local Access
allLimit access to SoftEther VPN management interface to trusted users only
Network Segmentation
allIsolate SoftEther VPN servers from critical network segments
🧯 If You Can't Patch
- Implement strict access controls to limit who can interact with the VPN management interface
- Monitor for unusual process creation or memory access patterns related to SoftEther VPN
🔍 How to Verify
Check if Vulnerable:
Check SoftEther VPN version via management console or by examining installed version. Version 5.02.5187 is vulnerable.Check Version:
On Windows: Check Programs and Features. On Linux: softether-vpnserver --version or check package manager.Verify Fix Applied:
Verify version is updated when patch becomes available. No current fix to verify.📡 Detection & Monitoring
Log Indicators:
- Unusual process crashes of vpnserver/vpnclient
- Memory access violation errors in application logs
- Multiple failed UI interaction attempts
Network Indicators:
- Unusual traffic patterns to/from VPN management ports
- Unexpected process spawning from VPN services
SIEM Query:
Process creation where parent process contains 'vpn' AND (command_line contains 'overflow' OR memory_access_violation = true)