In June 2022, Microsoft released a patch for a critical vulnerability tracked as CVE-2022-30154. This flaw affects the File Server Shadow Copy Agent Service, also known as RVSS, and opens the door for attackers to escalate their privileges on affected Windows systems. In this article, we break down what this vulnerability means, how it can be exploited, and what steps you can take to stay safe. We’ll also offer code snippets and resource links for further reading.

What Is RVSS?

The Remote Volume Shadow Copy Service (RVSS) helps administrators create shadow copies (point-in-time backups) of files on a server. It listens for remote procedure calls (RPCs) to help manage these copies across the network.

The Vulnerability in Simple Terms

CVE-2022-30154 is an Elevation of Privilege (EoP) vulnerability. This means a user or attacker with limited rights can leverage this flaw to gain higher-level permissions, like SYSTEM or Administrator on the target.

According to Microsoft

> *"An authenticated user could gain elevated privileges through a flaw in the File Server Shadow Copy Agent Service due to an improper check of user permissions."*

Potentially older supported Windows Server releases

See the full Microsoft Advisory for more details.

Step-by-Step Overview

1. Initial Access: An attacker must already have access to the target machine as a low-privileged user (or run code as such a user).
2. Abuse RVSS: By making carefully crafted RPC calls to the File Server Shadow Copy Agent Service, the attacker can bypass security checks.
3. Privilege Escalation: The flaw lets the attacker execute code with elevated (SYSTEM) privileges, granting full control over the server.

Example Code Snippet

Below is a conceptual Python snippet—not a working exploit!—showing how an attacker might interact with the VSS RPC endpoint using Windows named pipes. Note that such exploits are often written in C or PowerShell for direct API access, but this demonstrates the logic.

import win32pipe
import win32file

# This is *illustrative* and cannot be run as-is! 
# For demonstration only.

pipe_name = r'\\.\pipe\rvss'
try:
    # Connect to the pipe (acts as the RPC endpoint)
    pipe = win32file.CreateFile(
        pipe_name,
        win32file.GENERIC_READ | win32file.GENERIC_WRITE,
        ,  # No sharing
        None,
        win32file.OPEN_EXISTING,
        ,
        None
    )
    # Craft a malicious RPC payload that exploits the EoP flaw
    payload = b'...malicious_rpc_data...'
    win32file.WriteFile(pipe, payload)
    # Wait for response, privilege escalation occurs
    result = win32file.ReadFile(pipe, 4096)
    print("Exploit result:", result)
except Exception as e:
    print(f"Could not access RVSS pipe: {e}")

*Again, this is not a real exploit! It's a teaching example. The actual exploit interacts with VSS RPC structures and would likely use system calls unavailable in Python.*

Proof-of-Concept & Demonstrations

At the time of writing, no widely known public exploit is available, but security researcher Hacker House and others have discussed the vulnerability. (Check out the original GitHub issue for technical breakdowns).

The attacker connects to the RVSS service via named pipes.

- They exploit a flaw in ACL (Access Control List) enforcement, tricking the service into running code at a higher privilege.

How to Mitigate and Patch

If you manage a vulnerable system:  
- Immediately install June 2022 security updates from Windows Update or your patch management tool.  
 Microsoft’s official update guide for CVE-2022-30154

If you cannot patch immediately:

More Resources

- Microsoft Security Update Guide: CVE-2022-30154
- NIST NVD Detail
- Windows RPC and Named Pipes - MSDN Docs
- Security Research Example – Hacker House

Final Thoughts

CVE-2022-30154 shows how even internal services like RVSS can become serious security risks if access control is not enforced strictly. While this vulnerability requires local access, it’s a sharp reminder to patch regularly, restrict permissions, and monitor your environment for unusual activity.

If you are running an affected version of Windows Server, prioritize patching now. Stay safe!


*This post is written for educational purposes only. Do not attempt to exploit real systems without authorization.*

Timeline

Published on: 06/15/2022 22:15:00 UTC
Last modified on: 06/24/2022 21:04:00 UTC