CVE-2025-24991

What it actually does

CVE-2025-24991 is a local information disclosure vulnerability in the Windows NTFS file system driver caused by an out-of-bounds read. An attacker who already has authorized local access can trigger NTFS parsing or file-system operations in a way that reads memory outside the intended bounds, potentially exposing sensitive kernel or system memory contents. The flaw does not by itself provide remote code execution or initial access, but disclosed memory can be valuable for bypassing mitigations, weakening exploit protections, or supporting a larger local privilege escalation chain.

Why it matters to the business

Successful exploitation can expose sensitive information from Windows systems and may help attackers progress after they already have a foothold. Because this vulnerability is listed in CISA KEV, has active in-the-wild exploitation, and had a CISA remediation deadline of 2025-04-01, unpatched systems should be treated as a compliance and operational risk even though the CVSS score is moderate. The main business concern is not standalone disruption, but its usefulness as part of multi-step intrusions where attackers combine local information disclosure with credential theft, privilege escalation, or ransomware preparation.

How an attack unfolds

An attacker first obtains local access to a Windows system through valid credentials, malware execution, interactive logon, or another vulnerability. Once on the host, the attacker uses a specially crafted NTFS-related operation, file, volume, or disk image to trigger the out-of-bounds read in NTFS. The vulnerable driver reads beyond the intended memory boundary and returns or exposes data that should not be accessible to the attacker. The attacker then analyzes the disclosed information for useful memory addresses, kernel data, security-relevant values, or other sensitive artifacts. In a broader intrusion, this information may be used to improve reliability of another exploit, bypass memory protections, support local privilege escalation, or accelerate post-compromise activity. Microsoft and CISA have identified the vulnerability as exploited in the wild, so defenders should assume public or private exploitation techniques exist even if exploit details vary.

How to fix it

Apply the Microsoft security update that addresses CVE-2025-24991 for all supported Windows versions. Because the vulnerability is in NTFS, remediation requires operating system patching rather than application-level configuration changes. Prioritize internet-facing, multi-user, VDI, jump host, developer workstation, server, and high-value administrative systems where local access by many users or processes increases risk. If immediate patching is not possible, reduce exposure by restricting local interactive access, limiting use of untrusted removable media and mounted disk images, enforcing least privilege, blocking unknown executable content, and increasing monitoring for suspicious local exploit activity. Systems that cannot be patched should be isolated, access-controlled, and scheduled for upgrade or replacement. Since the CISA KEV due date was 2025-04-01, organizations subject to KEV-based remediation requirements should treat remaining exposure as overdue.

How to confirm the fix worked

Confirm that each Windows system has installed the Microsoft security update released for this vulnerability or a later cumulative update that supersedes it. Validate using Windows Update compliance tooling, endpoint management inventory, vulnerability scanners, or PowerShell-based checks of installed cumulative updates and OS build numbers against Microsoft’s official update guidance. Re-scan endpoints after deployment to ensure the vulnerability is no longer reported. Where compensating controls are used temporarily, validate that non-administrative local access is minimized, removable media and disk image handling are controlled, and EDR telemetry is available for NTFS-related suspicious activity. For high-risk systems, consider testing in a lab with the same OS build and patch level to confirm the vulnerable condition is no longer reproducible.

Typical attack path

1. Gain local access to a Windows system through phishing, stolen credentials, malware, remote service compromise, or physical/interactive access.
2. Identify that the host is running a vulnerable Windows build without the relevant Microsoft security update.
3. Stage or generate a crafted NTFS object, file-system operation, mounted image, or volume condition that reaches the vulnerable NTFS code path.
4. Trigger the NTFS out-of-bounds read from a local context.
5. Collect the disclosed memory or information returned by the vulnerable operation.
6. Use the leaked information to support follow-on exploitation, such as defeating exploit mitigations, improving a local privilege escalation attempt, or conducting additional post-exploitation activity.

How to detect it

Detection should focus on evidence of local post-compromise activity because exploitation requires authorized local access and may leave limited direct indicators. Review EDR telemetry, Windows event logs, crash reports, and file-system activity around suspicious user sessions. Relevant sources include Windows Security logs for local or remote logons, Sysmon or EDR process creation events, PowerShell and script execution logs, device control logs for removable media, events related to mounting VHD/VHDX/ISO files, and Windows Error Reporting or System logs for crashes or faults involving NTFS components. Look for unusual execution of disk, volume, or file-system utilities by non-administrative users; unexpected mounting of disk images; suspicious access to raw volumes; abnormal reads against NTFS volumes; and exploit chains followed by privilege escalation, credential dumping, or persistence. Because no universal public exploit string is guaranteed, detection should combine behavioral analytics with patch-state correlation: prioritize hosts that are both unpatched and show suspicious local file-system manipulation, crashes in NTFS-related components, or follow-on attacker behavior. If threat intelligence names specific campaigns or tools in the future, add those tool-specific hashes, command lines, and file artifacts to hunts.

• ntfs.sys
• NTFS_FILE_SYSTEM
• Ntfs
• fsutil
• mountvol
• diskpart
• vssadmin
• DeviceHarddiskVolume
• \.\PhysicalDrive
• \.\C:
• Mount-DiskImage
• VHD
• VHDX
• ISO

What your security team should do

• Treat this as urgent despite the moderate CVSS because it is in CISA KEV and has active in-the-wild exploitation; prioritize any remaining unpatched Windows systems immediately.
• Verify installation of the relevant Microsoft cumulative security updates across workstations, servers, VDI images, gold images, and offline templates.
• Hunt for suspicious local exploitation attempts on Windows hosts, especially where alerts show unusual mounted images, removable media usage, or crashes involving NTFS components.
• Correlate potential exploitation with signs of broader compromise, including privilege escalation attempts, credential dumping, suspicious child processes, and newly created persistence mechanisms.
• Restrict local logon rights and administrative privileges on systems that cannot be patched immediately.
• Increase scrutiny of hosts used by multiple users, exposed via remote access, or handling untrusted files and disk images.
• Document remediation status for KEV compliance and exception handling, noting that the CISA due date was 2025-04-01.