# Microsoft.Build.Tasks.Core .NET Spoofing Vulnerability

Advisory record · `GHSA-h4j7-5rxr-p4wc`

- **Identifiers:** `GHSA-h4j7-5rxr-p4wc` · `BIT-dotnet-2025-26646` · `BIT-dotnet-sdk-2025-26646` · `CVE-2025-26646`
- **State:** Confirmed
- **Severity:** CVSS 8.0 High
- **Critical:** No
- **Weakness (CWE):** [CWE-73](https://cwe.mitre.org/data/definitions/73.html)
- **Tags:** [Path traversal](https://agentprime.io/advisories/tag/path-traversal.md)
- **Published:** 13 May 2025
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 13 May 2025, 21:38 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `Microsoft.Build.Tasks.Core` (NuGet): affected `>=15.8.166, <15.9.30 || >=16.0.461, <16.11.6 || >=17.0.0, <17.8.29 || >=17.9.5, <17.10.29 || >=17.11.4, <17.12.36 || >=17.12.6, <17.13.26 || >=17.13.9, <17.14.8`; fixed in `15.9.30`, `16.11.6`, `17.8.29`, `17.10.29`, `17.12.36`, `17.13.26`, `17.14.8`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Microsoft.Build.Tasks.Core versions from 15.8.166 up to (but not including) the fixed releases 15.9.30, 16.11.6, 17.8.29, 17.10.29, 17.12.36, 17.13.26 and 17.14.8 are affected. The source describes external control of a file name or path that lets an unauthorized attacker perform spoofing over a network, though it gives few details on exact conditions. Projects that do not use the DownloadFile build task are stated not to be susceptible; otherwise, upgrade to the patched version for your release line.

Written 9 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.0 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`, from CNA (microsoft)

- **CISA KEV:** Not listed.
- **EPSS:** 0.013, the 70th percentile, on 11 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:21 UTC: First seen by agentprime
- 31 Oct 2026, 15:21 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-h4j7-5rxr-p4wc)

## Sources

- [GitHub Advisory Database: GHSA-h4j7-5rxr-p4wc](https://github.com/advisories/GHSA-h4j7-5rxr-p4wc)
- [OSV: GHSA-h4j7-5rxr-p4wc](https://osv.dev/vulnerability/GHSA-h4j7-5rxr-p4wc)
- <https://github.com/dotnet/msbuild/security/advisories/GHSA-h4j7-5rxr-p4wc>
- <https://nvd.nist.gov/vuln/detail/CVE-2025-26646>
- <https://github.com/dotnet/announcements/issues/356>
- <https://github.com/dotnet/msbuild/issues/11846>
- <https://github.com/dotnet/msbuild>
- <https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-26646>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-h4j7-5rxr-p4wc>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-h4j7-5rxr-p4wc/>. Everything for agents: <https://agentprime.io/llms.txt>.