# CVE-2026-2636: Denial of Service in Microsoft OS

> An unprivileged user can trigger a system crash in the CLFS.sys driver, causing a denial of service on affected Windows systems.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Feb 2026
- **Updated:** 26 Feb 2026
- **Also known as:** GHSA-fww6-3c6x-rf7p

## What is CVE-2026-2636?

CVE-2026-2636 is a medium-severity denial of service vulnerability in Microsoft Windows OS, published on 25 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

This vulnerability is caused by a CWE‑159: "Improper Handling of Invalid Use of Special Elements" weakness, which leads to an unrecoverable inconsistency in the CLFS.sys driver. This condition forces a call to the KeBugCheckEx function, allowing an unprivileged user to trigger a system crash. Microsoft silently fixed this vulnerability in the September 2025 cumulative update for Windows 11 2024 LTSC and Windows Server 2025. Windows 25H2 (released in September) was released with the patch. Windows 1123h2 and earlier versions remain vulnerable.

Weakness: CWE-159 (Improper Handling of Invalid Use of Special Elements)

## Which versions are affected by CVE-2026-2636?


## How do I fix CVE-2026-2636?

No fix has been published for CVE-2026-2636 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-2636 being exploited?

There is no known exploitation of CVE-2026-2636 in the wild and no public exploit code.

Public exploit code:

- **CVE-2026-2636** is a vulnerability in the Windows Common Log File System (CLFS) driver (`CLFS.sys`). An unprivileged user can trigger an unrecoverable system state by calling the `ReadFile` API on a handle opened via `CreateLogFile`. This results in a Blue Screen of Death (BSoD), leading to a denial of service (DoS) (github_poc): https://github.com/oxfemale/CVE-2026-2636_PoC
- https://github.com/uname1able/CVE-2026-2636 (github_poc): https://github.com/uname1able/CVE-2026-2636

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2636 and fix it if it is affected.

What it is: CVE-2026-2636 is a medium-severity denial of service vulnerability in Microsoft Windows OS, published on 25 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-2636 in the wild and no public exploit code.

Affected product: Microsoft Windows OS. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-2636/ (Markdown: https://insights.sbomify.com/CVE-2026-2636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2636
- OSV: https://osv.dev/vulnerability/CVE-2026-2636

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-2636/
Summaries are generated and may contain mistakes; the official description above is the record.