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PetitPotato

Local privilege escalation via PetitPotam (Abusing impersonate privileges).

Description

PetitPotam uses MS-EFSR (Encrypting File System Remote), a protocol used to perform maintenance and management operations on encrypted data stored remotely and accessed over a network. There are a series of APIs similar to EfsRpcOpenFileRaw in MS-EFSR. The syntax of the EfsRpcOpenFileRaw API is shown below.

long EfsRpcOpenFileRaw(
   [in] handle_t binding_h,
   [out] PEXIMPORT_CONTEXT_HANDLE* hContext,
   [in, string] wchar_t* FileName,
   [in] long Flags
 );

Such APIs can specify a UNC path via the FileName parameter to open encrypted objects on the server for backup or restore. When the path in the format \\IP\C$ is specified, the lsass.exe service will access \\IP\pipe\srvsvc with NT AUTHORITY SYSTEM account privileges.

If we can call the EfsRpcOpenFileRaw API to force the local computer to connect to the malicious named pipe we created, then we can impersonate the named pipe client process and eventually gain the SYSTEKM privilege.

But old PetitPotam does not work on newer versions of Windows due to the limitations of related patches. However, setting AuthnLevel to RPC_C_AUTHN_LEVEL_PKT_PRIVACY via RpcBindingSetAuthInfoW before calling EFS works on latest systems.

In December 2021, Microsoft released a patch for a different EFSRPC vulnerability: CVE-2021-43217. As part of the remediation for that issue, Microsoft implemented some hardening measures on EFSRPC communication. In particular, EFSRPC clients would need to use RPC_C_AUTHN_LEVEL_PKT_PRIVACY when using EFSRPC. If the client fails to do so, then the client is rejected and a Windows application event is generated.

At present, the project can perfectly elevate to SYSTEM on all versions of Windows (Test on Windows 21H2 10.0.20348.1547).

Usage

PetitPotato.exe [EfsID] [Command]

Example

C:\Users\Administrator\Desktop>PetitPotato.exe 3 cmd

[+] Malicious named pipe running on \\.\pipe\petit\pipe\srvsvc.
[+] Invoking EfsRpcQueryUsersOnFile with target path: \\localhost/pipe/petit\C$\wh0nqs.txt.
[+] The connection is successful.
[+] ImpersonateNamedPipeClient OK.
[+] OpenThreadToken OK.
[+] DuplicateTokenEx OK.
[+] CreateProcessAsUser OK.
Microsoft Windows [Version 10.0.20348.1547]
(c) Microsoft Corporation. All rights reserved.

C:\Windows\system32>whoami
nt authority\system

C:\Windows\system32>

image-20221030165055659

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