# CVE-2026-21249: Windows NTLM Spoofing Vulnerability

> An attacker can exploit external control of file names in Windows NTLM to perform local spoofing, bypassing security controls.

- **Severity:** Low 3.3 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 10 Feb 2026
- **Updated:** 19 Aug 2026
- **Also known as:** GHSA-w882-rf7q-923g

## What is CVE-2026-21249?

CVE-2026-21249 is a low-severity path traversal vulnerability in Microsoft Windows 10 1607, published on 10 Feb 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

External control of file name or path in Windows NTLM allows an unauthorized attacker to perform spoofing locally.

Weakness: CWE-73 (External Control of File Name or Path)

## Which versions are affected by CVE-2026-21249?

It affects 13 products.


Products: Microsoft Windows 10 1607, Microsoft Windows 10 1809, Microsoft Windows 10 21h2, Microsoft Windows 10 22h2, Microsoft Windows 11 23h2, Microsoft Windows 11 24h2, Microsoft Windows 11 25h2, Microsoft Windows Server 2012, Microsoft Windows Server 2016, Microsoft Windows Server 2019, Microsoft Windows Server 2022, Microsoft Windows Server 2022 23h2, Microsoft Windows Server 2025.

## How do I fix CVE-2026-21249?

No fix has been published for CVE-2026-21249 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21249 being exploited?

There is no known exploitation of CVE-2026-21249 in the wild and no public exploit code.

## Other vulnerabilities in Microsoft Windows 10 1607

- [CVE-2026-33824](https://insights.sbomify.com/CVE-2026-33824/): Microsoft Internet Key Exchange (IKE) Service Extensions Double Free (critical 9.8, exploited in the wild)
- [CVE-2026-21510](https://insights.sbomify.com/CVE-2026-21510/): Microsoft Windows Shell Protection Mechanism Failure (high 8.8, exploited in the wild)
- [CVE-2026-21513](https://insights.sbomify.com/CVE-2026-21513/): Microsoft MSHTML Framework Protection Mechanism Failure (high 8.8, exploited in the wild)
- [CVE-2023-32049](https://insights.sbomify.com/CVE-2023-32049/): Microsoft Windows Defender SmartScreen Security Feature Bypass (high 8.8, exploited in the wild)
- [CVE-2023-29360](https://insights.sbomify.com/CVE-2023-29360/): Microsoft Streaming Service Untrusted Pointer Dereference (high 8.4, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21249 and fix it if it is affected.

What it is: CVE-2026-21249 is a low-severity path traversal vulnerability in Microsoft Windows 10 1607, published on 10 Feb 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-21249 in the wild and no public exploit code.

Affected product: Microsoft Windows 10 1607. 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-2026-21249/ (Markdown: https://insights.sbomify.com/CVE-2026-21249/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21249
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21249
- OSV: https://osv.dev/vulnerability/CVE-2026-21249

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-21249/
Summaries are generated and may contain mistakes; the official description above is the record.