CVE-2023-23394: Revealing the Vulnerability in Client Server Run-Time Subsystem (CSRSS) - Laying Bare Crucial Details & Exploits

Security researchers have recently uncovered an information disclosure vulnerability in the Client Server Run-Time Subsystem (CSRSS), dubbed CVE-2023-23394. CSRSS is a critical component in Windows operating systems, responsible for console windows and creating and deleting threads. The vulnerability enables threat agents to gain access to sensitive user information, thus posing significant risk to affected systems.

In this post, we break down the exploit, including the vulnerable code snippet, along with the ramifications of the vulnerability. We'll also provide insight into the issue's background and share links to original references, ensuring you stay informed and up to date on this critical security flaw.

CVE-2023-23394 Vulnerability Explained

The vulnerability in CSRSS revolves around improper handling of certain system calls, leading to information disclosure. This potential security risk arises due to insecure usage of a shared memory section and weak parameter validation, which could allow a threat agent to retrieve sensitive information from the operating system's local memory.

The following code snippet highlights the point of vulnerability in the CSRSS system

NTSTATUS CsrpHandleVerifyRegionAccessRequest(
    PCSR_API_MSG Request,
    PCSR_REPLY_STATUS ReplyStatus
)
{
    HANDLE Process;
    PVOID BaseAddress;
    SIZE_T RegionSize;
    NTSTATUS Status;

    BaseAddress = Request->u.VerifyRegionAccessRequest.BaseAddress;
    RegionSize = Request->u.VerifyRegionAccessRequest.RegionSize;

    // Vulnerable point: Improper validation of BaseAddress and RegionSize parameters
    if (BaseAddress == NULL || RegionSize == )
    {
        Status = STATUS_INVALID_PARAMETER;
    }
    else
    {
        Process = ProcessIdToHandle(Request->h.ClientId.UniqueProcess);
        if (Process == NULL)
        {
            Status = STATUS_UNSUCCESSFUL;
        }
        else
        {
            Status = NtReadVirtualMemory(Process, BaseAddress,
                                          &LocalBuffer, RegionSize,
                                          &BytesRead));
            if (NT_SUCCESS(Status))
            {
                // Information disclosure exploit is executed here
            }
            NtClose(Process);
        }
    }

    return Status;
}

As we can see, the code snippet lacks proper validation checks for the BaseAddress and RegionSize parameters, paving the way for potential exploitation of the vulnerability.

Exploit Details

An attacker can exploit CVE-2023-23394 by crafting a malicious request using a specially designed application, which then calls the vulnerable system call. This approach allows the attacker to bypass the insufficient parameter validation and gain unauthorized access to the local memory, thereby amassing sensitive user information.

Implications & Recommended Actions

The information disclosure vulnerability in CSRSS leaves systems susceptible to a range of attacks, including data theft, privileged information access, and potentially even remote code execution. Organizations running an affected CSRSS version must take immediate action to curb potential threats by applying the appropriate security patch provided by the software vendor.

Original References & Further Information

For a comprehensive understanding of CVE-2023-23394, we encourage you to explore the following research resources:

1. CVE Details: CVE-2023-23394
2. National Vulnerability Database (NVD): CVE-2023-23394
3. Microsoft Security Update Guide: CVE-2023-23394

Closing Thoughts

The discovery of the information disclosure vulnerability in CSRSS is a timely reminder that even some of the most critical system components can be susceptible to security flaws. Implementing a proactive security approach that involves regular code review and security patch updates is crucial in safeguarding against potential security risks. Stay vigilant, and stay informed as new developments regarding CVE-2023-23394 emerge.

Timeline

Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/23/2023 16:59:00 UTC