A critical heap-based buffer overflow vulnerability, tracked as CVE-2025-24993, has been discovered in the Windows New Technology File System (NTFS), posing a significant threat to millions of Windows users globally.
The flaw, patched during Microsoft’s March 2025 Patch Tuesday, was actively exploited as a zero-day in the wild, prompting urgent advisories from both Microsoft and the U.S. Cybersecurity and Infrastructure Security Agency (CISA).
Exploit Chain and Attack Mechanics
CVE-2025-24993 arises from improper memory boundary validation in the NTFS driver when processing specially crafted Virtual Hard Disk (VHD) files.
The vulnerability is classified as a heap-based buffer overflow (CWE-122), which occurs when data written to a buffer on the heap exceeds its allocated size, potentially overwriting adjacent memory and enabling arbitrary code execution.
How the Exploit Works
- Trigger: Attackers craft a malicious VHD file, often disguised as a legitimate document or distributed via phishing campaigns and compromised USB drives.
- User Interaction: The exploit requires a user to mount the malicious VHD file, either through social engineering or by misleading the user into believing the file is safe.
- Vulnerability Activation: Upon mounting, the NTFS driver fails to properly check the boundaries of the memory buffer, allowing the attacker’s payload to overflow the heap and execute arbitrary code with the privileges of the local user.
- Impact: Successful exploitation can result in privilege escalation to SYSTEM-level access, full system compromise, data exfiltration, service disruption, and lateral movement within corporate networks.
Technical Summary Table
| Attribute | Details |
|---|---|
| CVE ID | CVE-2025-24993 |
| Vulnerability Type | Heap-based buffer overflow (CWE-122) |
| Attack Vector | Local (requires user to mount crafted VHD) |
| Privileges Required | None (but local access to mount VHD) |
| User Interaction | Required |
| CVSS Score | 7.8 (High) |
| Affected Systems | Windows 10, 11, Server editions (all supported NTFS versions) |
| Exploitation Status | Zero-day, actively exploited prior to patch |
| Patch Availability | Yes, March 2025 Patch Tuesday |
Code-Level Insight
While Microsoft has not released proof-of-concept (PoC) code, the vulnerability’s root cause lies in NTFS driver routines that handle VHD mounting.
A simplified pseudocode representation of the flawed logic might look like:
c// Pseudocode: Vulnerable NTFS VHD Mount Routine
void mount_vhd(char* vhd_data, size_t data_len) {
char* heap_buffer = malloc(FIXED_SIZE);
memcpy(heap_buffer, vhd_data, data_len); // No bounds check!
// ... further processing ...
}
In this example, if data_len exceeds FIXED_SIZE, the buffer overflow occurs, allowing attacker-controlled code to be injected into memory.
Mitigation, Detection, and Industry Response
Microsoft’s security update addresses the flaw by implementing stricter memory validation checks during VHD operations, preventing buffer overruns.
CISA has mandated federal agencies to patch all affected systems by April 1, 2025, and added the CVE to its Known Exploited Vulnerabilities Catalog.
Best Practices for Organizations:
- Deploy the March 2025 security patches across all Windows systems immediately.
- Educate users to avoid mounting unsolicited or suspicious VHD files, which are increasingly leveraged in phishing campaigns.
- Monitor endpoints for unusual VHD mounting activity and use advanced detection tools to flag anomalies.
- Segment networks to isolate legacy systems and limit the blast radius in case of compromise.
CVE-2025-24993 underscores the persistent risks associated with core file system components in modern operating systems.
Its exploitation as a zero-day highlights the critical need for rapid patch deployment, user education, and robust endpoint monitoring to safeguard against evolving cyber threats.
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