# Werkzeug safe_join() allows Windows special device names

Advisory record · `GHSA-g6x2-hccm-hh4m`

- **Identifiers:** `GHSA-g6x2-hccm-hh4m` · `CVE-2026-102598` · `PYSEC-2026-4312`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-67](https://cwe.mitre.org/data/definitions/67.html)
- **Tags:** [CWE-67](https://agentprime.io/advisories/tag/cwe-67.md)
- **Published:** 5 Oct 2026
- **Updated:** 15 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 5 Oct 2026, 23:48 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `werkzeug` (PyPI): affected `<3.1.9`; fixed in `3.1.9`

## Machine-written summary

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

> Werkzeug versions before 3.1.9 have a flaw in safe_join() that lets Windows device names through when they carry an empty ADS marker, such as NUL:. An attacker who can request files through an application's send_from_directory on Windows with NTFS can make reads hang indefinitely. Upgrade to Werkzeug 3.1.9 or later.

Written 1 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

- 6.3 Medium, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0037, the 31st percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:08 UTC: First seen by agentprime
- 31 Oct 2026, 14:08 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-g6x2-hccm-hh4m)

## Sources

- [GitHub Advisory Database: GHSA-g6x2-hccm-hh4m](https://github.com/advisories/GHSA-g6x2-hccm-hh4m)
- [OSV: GHSA-g6x2-hccm-hh4m](https://osv.dev/vulnerability/GHSA-g6x2-hccm-hh4m)
- <https://github.com/pallets/werkzeug/security/advisories/GHSA-g6x2-hccm-hh4m>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-102598>
- <https://github.com/pallets/werkzeug/pull/3309>
- <https://github.com/pallets/werkzeug/commit/8d77320bcdf3a34941ec06dcf16b03c065cd21b6>
- <https://github.com/pallets/werkzeug>
- <https://github.com/pallets/werkzeug/releases/tag/3.1.9>

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-g6x2-hccm-hh4m>, 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-g6x2-hccm-hh4m/>. Everything for agents: <https://agentprime.io/llms.txt>.