Recently, a new critical vulnerability dubbed "CVE-2022-21961" has been reported in Windows Resilient File System (ReFS). This vulnerability could allow an attacker to remotely execute malicious code on a target system. It's worth mentioning that this vulnerability is unique from other similar vulnerabilities such as CVE-2022-21892, CVE-2022-21928, CVE-2022-21958, CVE-2022-21959, CVE-2022-21960, CVE-2022-21962, and CVE-2022-21963. In this post, we will dissect the CVE-2022-21961 vulnerability, exploring its details, the exploit, and the potential impact on affected systems.

The underlying issue in the ReFS syscall handler

NTSTATUS RefsSyscallHandler(PKERNEL_BUFFER kbuf)
{
    NTSTATUS          status = STATUS_SUCCESS;
    PREMOTEFS_REQUEST Request = &kbuf->Request;

    status = SecurityCheck(Request); // An attacker may bypass this security check
    if(!NT_SUCCESS(status)) {
        return status;
    }
    ... // It proceeds to execute sensitive operations without further validation
}


An attacker may bypass the SecurityCheck() function, and then the syscall handler executes sensitive operations without further validation.

Original References

- CVE-2022-21961 in the National Vulnerability Database (NVD): https://nvd.nist.gov/vuln/detail/CVE-2022-21961
- Microsoft Security Response Center (MSRC) Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2022-21961

Exploit Details

The exploit hinges on the fact that an attacker can abuse the ReFS syscall handler by bypassing the security check. The intruder can then perform remote code execution without additional validation. To accomplish this, the attacker would typically send a crafted filesystem query with malicious contents. Once the query reaches the victim's ReFS syscall handler, the security check is bypassed, and the attacker gains control over critical operations on the target system.

The target user does not need to have elevated privileges for the attacker to exploit the vulnerability successfully. However, successful exploitation still hinges on the attacker sending specially crafted filesystem requests to the victim's device.

Potential Impact and Mitigation

The severity of this vulnerability cannot be overstated. Exploiting this vulnerability exposes the affected system to various potential consequences:

1. Remote code execution: The attacker may execute arbitrary code, resulting in severe data loss or compromising the system's security.
2. Escalation of Privileges: The attacker could potentially gain higher privileges, exacerbating the issue.
3. Data exfiltration and tampering: The attacker may access or modify sensitive data on the target system.

To mitigate the risk posed by this vulnerability, Microsoft has issued a security update that addresses the issue. Users and administrators should promptly apply the patch to avoid becoming victim to potential attacks. Additionally, maintaining good security hygiene by using a reputable anti-virus program and keeping your operating system updated can also go a long way in protecting your system from similar vulnerabilities.

Conclusion

CVE-2022-21961 is a critical vulnerability that affects the Windows Resilient File System (ReFS). Understanding how the vulnerability works, what the potential consequences are, and how to mitigate against an exploit is essential in safeguarding your systems. Staying informed and being proactive by applying appropriate patches and maintaining good security practices are the best ways to secure your systems against vulnerabilities like CVE-2022-21961.

Timeline

Published on: 01/11/2022 21:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC