CVE-2025-24993 - Heap-Based Buffer Overflow in Windows NTFS Explained (With Exploit Details)

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Introduction

On June 10, 2025, MITRE published CVE-2025-24993 — a critical heap-based buffer overflow vulnerability in Microsoft Windows NTFS (New Technology File System). This bug allows a local, unauthorized attacker to execute arbitrary code with elevated privileges. In this post, I’ll break down what this vulnerability is, how it’s exploited, and provide a simplified proof of concept for educational use.

What is CVE-2025-24993?

NTFS is the default file system for Windows. It manages how files are stored, named, and accessed on the disk. The vulnerability is caused by improper bounds checking in the way the NTFS driver processes certain on-disk metadata. An attacker with access to modify files can craft a special file (or disk image), causing the NTFS driver to overflow a buffer on the heap (dynamically-allocated memory). This can corrupt the driver's memory and allow code execution — essentially letting an attacker run malicious code on a Windows machine locally.

Affected Products:
- Windows 10, 11, and Windows Server 2019/2022 (all unpatched versions as of June 2025).

Attacker crafts a special NTFS file or disk image:

By manipulating the Master File Table (MFT), an attacker can cause NTFS.sys to process metadata that overflows an internal buffer. No network access is required: just local access (e.g., a user logging onto the Windows computer).

NTFS driver overflows heap buffer:

When Windows tries to read the malicious file, the NTFS driver allocates memory but writes more data than allocated, corrupting the heap.

Executing code:

Carefully crafted data can overwrite important pointers on the heap, redirecting execution (e.g., to a shellcode payload).

Sample Proof-of-Concept (PoC) Code

Here’s a simplified experiment in C — do NOT use in production or on systems you care about!. This represents how an attacker might trigger a heap buffer overflow in a C program (not real kernel code, just a teaching example!).

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void vulnerable_function(const char* input) {
    // Heap buffer: intended for 64 bytes
    char *heap_buf = (char*)malloc(64);
    if (!heap_buf) exit(1);

    // BAD: Copies untrusted input with no length check
    strcpy(heap_buf, input);

    printf("Heap buffer now contains: %s\n", heap_buf);
    free(heap_buf);
}

int main(int argc, char **argv) {
    if (argc != 2) {
        printf("Usage: %s <input>\n", argv[]);
        return 1;
    }

    vulnerable_function(argv[1]);
    return ;
}

How this relates

- The Windows NTFS driver performs a similar *unsafe* operation (without checking lengths) when parsing certain structures.

Impact & Mitigation

- Attack Type: Local, no user interaction needed (except access to plug a USB or create virtual disk).
- Impact: Full system compromise, privilege escalation, or remote code execution via lateral movement.
- Patches: Microsoft released a security update on June 12, 2025.

If you haven’t patched yet:
- Disable autorun for USB/media mounts.

References & Further Reading

- MITRE CVE-2025-24993 Entry
- Microsoft Security Advisory
- Basics of Heap Overflows
- How NTFS Works

Conclusion

CVE-2025-24993 shows how file system bugs can become system compromises. This highlights why low-level driver code needs tight bounds checking and why users should apply security updates ASAP. If you’re on Windows, patch your systems now. For researchers: always build and test on isolated machines.

Timeline

Published on: 03/11/2025 17:16:35 UTC
Last modified on: 03/23/2025 16:12:30 UTC