What is CVE-2025-29824?
This is a use‑after‑free flaw in the Microsoft Windows Common Log File System (CLFS) driver. An authorised attacker who can run code on the machine can trigger the bug and gain higher privileges. The National Vulnerability Database rates it at 7.8, which is in the HIGH range.
Related remediation guides
Other vulnerabilities in the same family or affecting the same products:
- CVE-2024-49039 – Windows Task Scheduler privilege escalation fix guide
- CVE-2021-43226 – Windows CLFS Driver Privilege Escalation – What You Need to Do
- CVE-2026-6875 – ServiceNow AI Platform Remote Code Execution – What You Need to Do
For the wider picture, our Known Exploited Vulnerabilities tracker lists every flaw CISA has confirmed under active attack.
Who should care?
If you run any Windows desktop or server version that ships the CLFS driver – essentially every supported Windows 10, Windows 11 and Windows Server release – you need to read on. The vulnerability is confirmed to be exploited in the wild and has been used by ransomware groups. If you manage a fleet of workstations, laptops or cloud‑hosted VMs, this is directly relevant.
How the vulnerability works
The CLFS driver handles structured log files for a number of Windows components. Internally it allocates memory for log entries, then later frees that memory when the entry is no longer needed. The flaw occurs when the driver frees the memory but continues to use a pointer that now points to reclaimed space. An attacker who can cause the driver to process a crafted log record can cause the driver to dereference the stale pointer.
Because the driver runs in kernel mode, the dereference happens with full system privileges. By carefully arranging the contents of the reclaimed memory, the attacker can cause the kernel to execute code of their choosing. The result is a local privilege‑escalation – a low‑privilege user ends up with SYSTEM or Administrator rights.
Microsoft has not released a detailed technical write‑up of the exploit chain. The public description is limited to “use‑after‑free” and “privilege escalation”. That is typical for a vulnerability that is already being abused; the exact payload construction is kept under wraps to avoid giving attackers more guidance.
How to check if you are exposed
The easiest way to know whether your machine is vulnerable is to compare the build number of your OS against the list of fixed releases. Microsoft publishes the fix as a cumulative update for each Windows branch. The table below, pulled automatically from the NVD, shows the last vulnerable build for each branch and the first build that contains the fix.
To see your current build, open a command prompt and run:
systeminfo | findstr /B /C:"OS Version"
or, on newer systems, use:
winver
The output will contain a version string like “10.0.xxxxx.xxxxx”. Do not try to match the exact numbers yourself – simply note the build and compare it to the table. If your build appears in the “up to” column, you are still vulnerable and need to apply the update.
Mitigation and remediation steps
Microsoft has released patches for every affected branch. The recommended action is to install the latest cumulative update for your Windows edition. This brings the CLFS driver to the patched state.
Step‑by‑step patching
- Windows Update: Open Settings → Update & Security → Windows Update and click “Check for updates”. Install any available cumulative updates. This method works for most desktops and laptops.
- WSUS / SCCM: If you manage updates centrally, approve the latest cumulative update for the appropriate product group. Deploy it as you would any other security patch.
- PowerShell: For quick remote remediation, run the following on each target:
Invoke‑Command -ComputerName $env:COMPUTERNAME -ScriptBlock { Install‑Module -Name PSWindowsUpdate -Force; Import‑Module PSWindowsUpdate; Install‑WindowsUpdate -AcceptAll -AutoReboot } - Manual download: If you cannot use Windows Update, download the appropriate package from the Microsoft Update Catalog. Search for “CVE-2025-29824” or the KB that addresses the CLFS driver. Install the.msu file with
wusa.exe /quiet /norestart.
After the update, reboot the machine. Verify the build number again – it should now be newer than the “up to” entry in the table.
Temporary mitigations
If, for any reason, you cannot apply the update immediately, consider these short‑term controls:
- Restrict local logon rights. Only trusted administrators should have interactive access.
- Disable any service that writes to CLFS logs and is not essential. This reduces the attack surface, though it may impact functionality.
- Enable Device Guard or Credential Guard where available. These harden the kernel and can block some exploitation attempts.
- Monitor the event log for unusual driver load events or attempts to access CLFS files. A sudden spike could indicate an attacker probing the flaw.
These mitigations do not replace the patch – they only buy you time.
If you cannot patch immediately
In rare cases a system may be locked to a specific build (for example, an embedded device or a legacy application that cannot run a newer cumulative update). The guidance from CISA is clear: either apply the vendor‑provided mitigation, follow the BOD 22‑01 guidance for cloud workloads, or discontinue use of the product.
For cloud‑hosted Windows VMs, the same patching process applies – most cloud providers push the cumulative update as part of their regular maintenance windows. Verify with your provider that the latest patch is applied to the image you are using.
If you must keep an unpatched system running, isolate it from the rest of the network. Use a VLAN with no access to sensitive resources, and block inbound traffic on ports that are not required. Treat the machine as a high‑risk asset and monitor it closely.
What to do after remediation
Once the patch is installed, run a quick check to confirm the build is no longer listed as vulnerable. Then, update your asset inventory to mark the host as patched for CVE-2025-29824. If you use a vulnerability scanner, re‑run the scan to verify the finding disappears.
Finally, document the incident response steps you took. This helps audit teams and satisfies any compliance requirement that asks for proof of remediation.
Summary
CVE-2025-29824 is a high‑severity, confirmed‑in‑the‑wild use‑after‑free bug in the Windows CLFS driver that allows local privilege escalation. All supported Windows 10, Windows 11 and Windows Server releases are listed as affected. The fix is available as a cumulative update for each branch. Check your build number, apply the latest update, reboot, and verify. If you cannot patch, apply the temporary mitigations, isolate the machine, or retire it. The table below shows the exact range of vulnerable and patched builds – use it as your reference point.
Affected versions
Straight from the NVD record for CVE-2025-29824. If your build is inside one of these ranges, treat it as vulnerable.
| Product | Affected range | Fixed in |
|---|---|---|
windows_10_1507 |
* up to 10.0.10240.20978 | 10.0.10240.20978 |
windows_10_1607 |
* up to 10.0.14393.7969 | 10.0.14393.7969 |
windows_10_1809 |
* up to 10.0.17763.7136 | 10.0.17763.7136 |
windows_10_21h2 |
* up to 10.0.19044.5737 | 10.0.19044.5737 |
windows_10_22h2 |
* up to 10.0.19045.5737 | 10.0.19045.5737 |
windows_11_22h2 |
* up to 10.0.22621.5189 | 10.0.22621.5189 |
windows_11_23h2 |
* up to 10.0.22631.5189 | 10.0.22631.5189 |
windows_11_24h2 |
* up to 10.0.26100.3775 | 10.0.26100.3775 |
windows_server_2016 |
* up to 10.0.14393.7969 | 10.0.14393.7969 |
windows_server_2019 |
* up to 10.0.17763.7136 | 10.0.17763.7136 |
windows_server_2022 |
* up to 10.0.20348.3453 | 10.0.20348.3453 |
windows_server_2022_23h2 |
* up to 10.0.25398.1551 | 10.0.25398.1551 |
