Fast FAT Vulnerability in Microsoft Windows Exploited in the Wild – CISA

A critical integer overflow vulnerability (CVE-2025-24985) in Microsoft’s Windows Fast FAT File System Driver has prompted urgent warnings from cybersecurity authorities.

Rated 7.8 on the CVSS scale, this flaw enables local code execution via physical attacks, requiring attackers to mount malicious virtual hard drives (VHDs) on compromised systems.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added the vulnerability to its Known Exploited Vulnerabilities (KEV) catalog, mandating federal agencies to apply patches by April 1, 2025.

Exploitation Mechanics and Risks

The vulnerability stems from improper handling of integer arithmetic in the Fast FAT driver, a legacy component managing FAT/FAT32 file systems.

Attackers exploiting this flaw could craft malicious VHD files to trigger an integer overflow, leading to memory corruption and arbitrary code execution.

While physical access is required, the threat remains significant for high-value targets like government agencies or critical infrastructure.

Notably, this marks the first actively exploited zero-day in the Fast FAT driver since March 2022.

Although no ransomware campaigns have been linked to CVE-2025-24985 yet, its potential for abuse in targeted attacks raises concerns.

Researchers warn that attackers could chain this flaw with privilege escalation vulnerabilities—such as CVE-2025-24983—to gain full system control.

Mitigation Strategies and Industry Response

Microsoft addressed the vulnerability in its March 2025 Patch Tuesday update, which resolved 57 security flaws, including six critical and six exploited zero-days.

Key recommendations include:

• Apply updates immediately: Install the latest security patches for Windows systems.
• Restrict VHD usage: Block unauthorized mounting of virtual drives via Group Policy or endpoint protection tools.
• Monitor for anomalies: Deploy solutions like SOCRadar’s Attack Surface Management to detect suspicious activity.

CISA emphasizes adherence to Binding Operational Directive (BOD) 22-01 for cloud environments, urging organizations to disable affected services if patching isn’t feasible.

Satnam Narang of Tenable notes, “This vulnerability underscores the risks posed by legacy components in modern systems, especially when paired with social engineering tactics”.

The anonymous disclosure of CVE-2025-24985 and related NTFS flaws highlights ongoing challenges in securing foundational Windows subsystems.

With federal remediation deadlines looming, proactive defense remains critical to thwarting advanced persistent threats.

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