hacktricks/windows-hardening/windows-local-privilege-escalation/appenddata-addsubdirectory-permission-over-service-registry.md

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**The original post is** [**https://itm4n.github.io/windows-registry-rpceptmapper-eop/**](https://itm4n.github.io/windows-registry-rpceptmapper-eop/)

## Summary

Two registry keys were found to be writable by the current user:

- **`HKLM\SYSTEM\CurrentControlSet\Services\Dnscache`**
- **`HKLM\SYSTEM\CurrentControlSet\Services\RpcEptMapper`**

It was suggested to check the permissions of the **RpcEptMapper** service using the **regedit GUI**, specifically the **Advanced Security Settings** window's **Effective Permissions** tab. This approach enables the assessment of granted permissions to specific users or groups without the need to examine each Access Control Entry (ACE) individually.

A screenshot showed the permissions assigned to a low-privileged user, among which the **Create Subkey** permission was notable. This permission, also referred to as **AppendData/AddSubdirectory**, corresponds with the script's findings.

The inability to modify certain values directly, yet the capability to create new subkeys, was noted. An example highlighted was an attempt to alter the **ImagePath** value, which resulted in an access denied message.

Despite these limitations, a potential for privilege escalation was identified through the possibility of leveraging the **Performance** subkey within the **RpcEptMapper** service's registry structure, a subkey not present by default. This could enable DLL registration and performance monitoring.

Documentation on the **Performance** subkey and its utilization for performance monitoring was consulted, leading to the development of a proof-of-concept DLL. This DLL, demonstrating the implementation of **OpenPerfData**, **CollectPerfData**, and **ClosePerfData** functions, was tested via **rundll32**, confirming its operational success.

The goal was to coerce the **RPC Endpoint Mapper service** into loading the crafted Performance DLL. Observations revealed that executing WMI class queries related to Performance Data via PowerShell resulted in the creation of a log file, enabling the execution of arbitrary code under the **LOCAL SYSTEM** context, thus granting elevated privileges.

The persistence and potential implications of this vulnerability were underscored, highlighting its relevance for post-exploitation strategies, lateral movement, and evasion of antivirus/EDR systems.

Although the vulnerability was initially disclosed unintentionally through the script, it was emphasized that its exploitation is constrained to outdated Windows versions (e.g., **Windows 7 / Server 2008 R2**) and requires local access.

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