CVE-2023-36405 - Windows Kernel Elevation of Privilege Vulnerability Explained

If you’re following Windows security, you may have heard about CVE-2023-36405—a Windows Kernel elevation of privilege vulnerability disclosed and patched by Microsoft. In this post, we’ll break down what this vulnerability is, how it works, show some example code, and explain what you can do to stay secure. We’ll also link to official references for deeper reading.

What is CVE-2023-36405?

CVE-2023-36405 is a security vulnerability identified in the Windows Kernel, the core of the Windows operating system. The vulnerability can allow an attacker to escalate privileges from a regular user account to SYSTEM, which is the highest privilege level on Windows.

Severity: High
CVSS Score: 7.8 (High)
Published: June 2023
Patched: Yes, in June 2023 Patch Tuesday updates.

In Simple Terms

If an attacker already has access to a computer (as a limited user), CVE-2023-36405 lets them break out of that “box” and potentially take full control of the system. This means they could read or modify any file, install software, or even create new admin users.

How the Vulnerability Works

The CVE boils down to the Windows Kernel not correctly handling some operations involving internal objects (like tokens or handles). Through a series of steps, an attacker can abuse this mistake to “impersonate” the SYSTEM user, effectively granting themselves admin rights.

Local Access Needed: The attacker needs to run code on the target machine.

2. Trigger the Bug: They use specially crafted code to interact with a vulnerable system call (common ones include NtCreateSection or similar Windows Native APIs).
3. Privilege Escalation: They manipulate the way the kernel allocates or assigns permissions, tricking Windows into treating them as SYSTEM.

Exploit Example (Pseudo-code)

Below is a *simplified* and *educational* example, showing the kind of logic an attacker might use. Do not use this for malicious purposes—the code is for illustration only.

Step 1: Abusing a Vulnerable System Call

#include <windows.h>
#include <stdio.h>

// This is just an example! It does not exploit the actual CVE.
int main() {
    HANDLE hToken;
    // STEP 1: Get a handle to your own user token
    if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken)) {
        printf("Could not open token.\n");
        return 1;
    }

    // STEP 2: Try to adjust the token (normally restricted)
    TOKEN_PRIVILEGES tp;
    tp.PrivilegeCount = 1;  
    LookupPrivilegeValue(NULL, SE_DEBUG_NAME, &tp.Privileges[].Luid);  
    tp.Privileges[].Attributes = SE_PRIVILEGE_ENABLED;  

    if (!AdjustTokenPrivileges(hToken, FALSE, &tp, sizeof(tp), NULL, NULL)) {
        printf("Could not enable privilege.\n");
        return 1;
    }

    // From here, the exploit would use a system call to interact with the kernel
    // and escalate to SYSTEM privileges by exploiting the vulnerability.
    // This code is only demonstrative!
    printf("Privilege adjusted (if exploit is successful, you'd be SYSTEM now!)\n");
    
    return ;
}

Again, the real exploit involves more advanced kernel-level tricks and would not be as simple as this, but this gives you the general idea.

Step 3: Move laterally or maintain persistence using full admin rights.

Note: This vulnerability cannot be exploited remotely; attackers must already have some form of access.

References

- Microsoft Security Guide for CVE-2023-36405
- NVD – National Vulnerability Database: CVE-2023-36405
- Microsoft’s June 2023 Patch Tuesday Release Notes

Limit User Accounts: Don’t use admin accounts for daily activities.

- Monitor for Unusual Activity: Use endpoint security solutions that can spot privilege escalation.
- Educate Yourself and Staff: Be wary of phishing and unsafe downloads, as these often provide the “first step” attackers need.

Conclusion

CVE-2023-36405 is a serious elevation of privilege bug in the Windows Kernel that allows attackers with local access to gain full control of affected systems. Microsoft has patched the issue, so staying up-to-date is your best defense. Understanding the risk and how these bugs work is key to keeping your organization safe.

Feel free to share this post with colleagues and friends who want to know more about Windows security!


*This post is exclusive and simplified for general readers. For more technical details, always consult the original references.*

Timeline

Published on: 11/14/2023 18:15:42 UTC
Last modified on: 11/20/2023 20:23:24 UTC