# CVE-2026-42904: Windows TCP/IP Elevation of Privilege Vulnerability

> Heap-based buffer overflow in Windows TCP/IP allows adjacent network attackers to elevate privileges.

- **Severity:** Critical 9.6 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/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:** Not needed
- **Fix available:** No
- **Published:** 9 Jun 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-3f78-xrf3-9xc8

## What is CVE-2026-42904?

CVE-2026-42904 is a critical memory corruption vulnerability in Microsoft Windows 10 21h2, published on 9 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Heap-based buffer overflow in Windows TCP/IP allows an unauthorized attacker to elevate privileges over an adjacent network.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-42904?

It affects 8 products.


Products: Microsoft Windows 10 21h2, Microsoft Windows 10 22h2, Microsoft Windows 11 23h2, Microsoft Windows 11 24h2, Microsoft Windows 11 25h2, Microsoft Windows 11 26h1, Microsoft Windows Server 2022, Microsoft Windows Server 2025.

## How do I fix CVE-2026-42904?

No fix has been published for CVE-2026-42904 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42904 being exploited?

There is no known exploitation of CVE-2026-42904 in the wild and no public exploit code.

## Other vulnerabilities in Microsoft Windows 10 21h2

- [CVE-2025-21333](https://insights.sbomify.com/CVE-2025-21333/): Microsoft Windows Hyper-V NT Kernel Integration VSP Heap-based Buffer Overflow (high 7.8, exploited in the wild)
- [CVE-2025-21334](https://insights.sbomify.com/CVE-2025-21334/): Microsoft Windows Hyper-V NT Kernel Integration VSP Use-After-Free (high 7.8, exploited in the wild)
- [CVE-2025-21335](https://insights.sbomify.com/CVE-2025-21335/): Microsoft Windows Hyper-V NT Kernel Integration VSP Use-After-Free (high 7.8, exploited in the wild)
- [CVE-2026-105733](https://insights.sbomify.com/CVE-2026-105733/): Windows Hyper-V Remote Code Execution Vulnerability (high 8.8)
- [CVE-2026-69945](https://insights.sbomify.com/CVE-2026-69945/): Windows AppX Deployment Extensions Elevation of Privilege Vulnerability (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42904 and fix it if it is affected.

What it is: CVE-2026-42904 is a critical memory corruption vulnerability in Microsoft Windows 10 21h2, published on 9 Jun 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-2026-42904 in the wild and no public exploit code.

Affected product: Microsoft Windows 10 21h2. 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-2026-42904/ (Markdown: https://insights.sbomify.com/CVE-2026-42904/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42904
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42904
- OSV: https://osv.dev/vulnerability/CVE-2026-42904

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42904/
Summaries are generated and may contain mistakes; the official description above is the record.