Security researchers have identified a new elevation of privilege (EoP) vulnerability in the Microsoft File Server Shadow Copy Agent Service (RVSS). This vulnerability, known as CVE-2022-30154, poses serious risks to your file server, potentially allowing an attacker to gain unauthorized administrative privileges and control, carrying out malicious actions, such as installing programs, altering data, or creating new accounts with full user rights. In this in-depth analysis, we will examine the exploit and offer guidance on potential remediation steps.

Exploit Details

CVE-2022-30154 targets the RVSS service, which manages shadow copies of Windows file servers. The vulnerability lies in the improper handling of symbolic links (symlinks) by the implemented service. A symlink is a file that contains a reference to another file or directory; think of it as a shortcut that links to another location on the network.

If an attacker successfully exploits this, they could potentially manipulate vulnerable systems into creating a symlink that references a protected resource. The attacker provides a symlink to a low-privileged component, such as a log file, which is then processed by the vulnerable high-privileged process. By leveraging the service's high privileges, the attacker can then overwrite critical system data, effectively bypassing any protection mechanisms, and elevating their privileges.

Proof-of-Concept (PoC) Exploit

To better understand this vulnerability, let's take a look at a high-level proof-of-concept developed by researchers:

1. First, the attacker modifies their low-privileged component (such as a log file) to point to a symlink file. This file can include any resource under the control of the attacker.

echo "_Parameter_" > C:\evil\evil.log

2. Then, the attacker creates a symlink that links to a critical system location that should be protected from modification by low-privileged users.

mklink /h "C:\evil\symlink" "%WINDIR%\system32\critical\system_data"

3. Finally, the attacker triggers the vulnerable component using standard Windows APIs to overwrite the targeted critical system data, causing the elevation of privileges.

HKEY hKey = NULL;
LONG status = RegOpenKeyEx(HKEY_LOCAL_MACHINE, "SYSTEM\\CurrentControlSet\\Services\\VssAgent", , KEY_ALL_ACCESS, &hKey);

if (status == ERROR_SUCCESS) {
    RegSetValueEx(hKey, "ImagePath", , REG_EXPAND_SZ, (BYTE *)"\\??\\C:\\evil\\symlink", (DWORD)((lstrlen("\\??\\C:\\evil\\symlink") + 1) * sizeof(TCHAR)));
    RegCloseKey(hKey);
}

To learn more about CVE-2022-30154, visit the original source from the CVE database here: Link to CVE Database Entry

Remediation and Consequences

As of now, Microsoft has not released an official patch for CVE-2022-30154. While we wait for Microsoft to release an update, you should consider implementing the following mitigation techniques to safeguard your systems:

Disable the File Server Shadow Copy Agent Service (RVSS) if it is not required for your environment.

2. Apply the Principle of Least Privilege (PoLP) and restrict user access on all systems. Limit the number of users with administrative privileges.
3. Regularly update and patch all systems and software to ensure that you are protected against known vulnerabilities.
4. Implement strong monitoring and logging policies to detect and track any unauthorized activity on your networks and systems.

Failure to address this vulnerability could have drastic consequences, including unauthorized access to sensitive data, compromised user accounts, and further distribution of malware via the exploited system.

Conclusion

CVE-2022-30154 is a serious vulnerability with the potential to give an attacker unauthorized access to and control over a targeted Windows file server. Understanding the exploit, implementing remediation measures, and staying vigilant are crucial steps in ensuring the ongoing security of your organization. We'll continue to monitor this vulnerability and provide updates as new information and fixes become available.

References

- CVE-2022-30154 CVE Database Entry
- Microsoft Security Advisory

Timeline

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