CVE-2025-24985 Overview
CVE-2025-24985 is an integer overflow or wraparound vulnerability in the Windows Fast FAT Driver that allows an unauthorized attacker to execute code locally. This vulnerability affects the kernel-level file system driver responsible for handling FAT (File Allocation Table) formatted storage media, making it particularly dangerous as successful exploitation can lead to complete system compromise with elevated privileges.
Critical Impact
This vulnerability is actively exploited in the wild and is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Organizations must prioritize patching immediately as attackers can achieve arbitrary code execution through crafted FAT file system images.
Affected Products
- Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
- Microsoft Windows Server 2008 SP2, 2008 R2 SP1, 2012, 2012 R2, 2016, 2019, 2022, 2022 23H2, 2025
Discovery Timeline
- March 11, 2025 - CVE-2025-24985 published to NVD
- October 27, 2025 - Last updated in NVD database
Technical Details for CVE-2025-24985
Vulnerability Analysis
The vulnerability exists within the Windows Fast FAT Driver (fastfat.sys), a kernel-mode driver responsible for parsing and mounting FAT12, FAT16, and FAT32 file systems. The integer overflow condition occurs when the driver processes specially crafted metadata within a FAT file system image, specifically when calculating memory buffer sizes or array indices during file system mounting operations.
When an integer overflow occurs in a kernel driver, the calculated value wraps around to a smaller-than-expected value. This can result in undersized buffer allocations (CWE-122: Heap-based Buffer Overflow) that are subsequently overwritten with attacker-controlled data, leading to heap corruption in kernel memory space. The associated CWE-190 (Integer Overflow or Wraparound) classification confirms the root cause of this vulnerability.
Root Cause
The root cause is an integer overflow (CWE-190) in the Windows Fast FAT Driver during arithmetic operations on file system metadata fields. When processing FAT volume boot sector parameters or directory entry calculations, the driver performs multiplication or addition operations on user-controlled values without adequate bounds checking. When these operations produce results exceeding the maximum value for the data type, the value wraps around to a small positive integer, leading to a heap-based buffer overflow (CWE-122) when undersized buffers are subsequently populated with file system data.
Attack Vector
The attack vector is local, requiring user interaction to mount a malicious storage device or FAT-formatted image file. An attacker can deliver the malicious FAT file system image through several methods:
- Physical media: USB drives, SD cards, or other removable storage formatted with a malicious FAT image
- Virtual disk images: VHD, VHDX, or raw disk images containing crafted FAT partitions
- Email attachments: Disk image files sent as attachments that users may mount
- Downloaded archives: Malicious disk images distributed through file sharing or compromised websites
When a user mounts the malicious file system, the Windows Fast FAT Driver parses the crafted metadata, triggering the integer overflow condition and enabling arbitrary code execution in kernel mode.
Detection Methods for CVE-2025-24985
Indicators of Compromise
- Unexpected mounting of FAT-formatted volumes from untrusted sources
- Crash dumps indicating fastfat.sys driver failures or memory corruption
- Suspicious VHD, VHDX, or raw disk image files appearing on systems
- Unusual kernel-mode activity following USB device insertion events
Detection Strategies
- Monitor Windows Event Logs for unexpected removable storage mount events (Event IDs 2003, 2100, 2101 in Microsoft-Windows-Partition/Diagnostic)
- Deploy endpoint detection rules for suspicious file system image file creation or access patterns
- Enable kernel debugging and driver verifier to detect heap corruption in fastfat.sys
- Implement behavioral analysis for privilege escalation attempts following media mount operations
Monitoring Recommendations
- Enable Windows Defender Exploit Guard Attack Surface Reduction rules for USB device restrictions
- Configure centralized logging for all removable media mount events across the enterprise
- Deploy SentinelOne agents with Deep Visibility to track kernel driver activity and file system operations
- Monitor for anomalous process creation chains originating from file system mount operations
How to Mitigate CVE-2025-24985
Immediate Actions Required
- Apply the latest Microsoft security updates from the March 2025 Patch Tuesday release immediately
- Restrict removable media usage through Group Policy until patches are deployed
- Block mounting of untrusted VHD/VHDX files via Windows Defender Application Control policies
- Audit systems for any indicators of compromise related to this vulnerability
Patch Information
Microsoft has released security updates to address this vulnerability. Organizations should obtain the appropriate patches from the Microsoft Security Update Guide for CVE-2025-24985. Given that this vulnerability is actively exploited and listed in the CISA Known Exploited Vulnerabilities Catalog, federal agencies and critical infrastructure organizations should follow CISA's binding operational directives for remediation timelines.
Workarounds
- Disable automatic mounting of removable storage devices via Group Policy (Computer Configuration > Administrative Templates > System > Removable Storage Access)
- Restrict USB device usage to approved devices only using endpoint protection policies
- Deploy application control policies to prevent mounting of disk image files from untrusted locations
- Consider temporarily disabling the FAT file system driver in high-security environments where FAT support is not required
# PowerShell: Disable Removable Storage Access via Registry
Set-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\RemovableStorageDevices" -Name "Deny_All" -Value 1 -Type DWord
# Verify the setting
Get-ItemProperty -Path "HKLM:\SOFTWARE\Policies\Microsoft\Windows\RemovableStorageDevices" -Name "Deny_All"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
