# Mako: Path traversal via drive-letter URI on Windows in TemplateLookup

Advisory record · `GHSA-5639-2j2p-m4mx`

- **Identifiers:** `GHSA-5639-2j2p-m4mx` · `CVE-2026-102991` · `PYSEC-2026-4243`
- **State:** Confirmed
- **Severity:** CVSS 6.5 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-22](https://cwe.mitre.org/data/definitions/22.html)
- **Tags:** [Path traversal](https://agentprime.io/advisories/tag/path-traversal.md)
- **Published:** 5 Oct 2026
- **Updated:** 15 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 5 Oct 2026, 23:42 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `mako` (PyPI): affected `<1.4.2`; fixed in `1.4.2`

## Machine-written summary

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

> Mako versions before 1.4.2 are vulnerable on Windows when a TemplateLookup URI begins with a drive designator such as C:/ or C:\\, which bypasses the directory traversal check. An attacker who can influence template names or include paths passed to TemplateLookup.get_template() can read files outside the template directory, and may execute them if they contain Mako template syntax. Upgrade to Mako 1.4.2 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

- 6.5 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0036, the 29th percentile, on 8 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-5639-2j2p-m4mx)

## Sources

- [GitHub Advisory Database: GHSA-5639-2j2p-m4mx](https://github.com/advisories/GHSA-5639-2j2p-m4mx)
- [OSV: GHSA-5639-2j2p-m4mx](https://osv.dev/vulnerability/GHSA-5639-2j2p-m4mx)
- <https://github.com/sqlalchemy/mako/security/advisories/GHSA-5639-2j2p-m4mx>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-102991>
- <https://github.com/sqlalchemy/mako/issues/441>
- <https://github.com/sqlalchemy/mako/commit/000ed85e4e48771eff460bf4fc721fb43de80e08>
- <https://github.com/sqlalchemy/mako>
- <https://github.com/sqlalchemy/mako/releases/tag/rel_1_4_2>

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-5639-2j2p-m4mx>, 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-5639-2j2p-m4mx/>. Everything for agents: <https://agentprime.io/llms.txt>.