# Copier has a trust-prefix bypass via path traversal that runs tasks unprompted

Advisory record · `GHSA-9gmc-jqmh-3rvm`

- **Identifiers:** `GHSA-9gmc-jqmh-3rvm` · `CVE-2026-53951` · `PYSEC-2026-3818`
- **State:** Confirmed
- **Severity:** CVSS 8.8 High
- **Critical:** No
- **Weakness (CWE):** [CWE-22](https://cwe.mitre.org/data/definitions/22.html) · [CWE-94](https://cwe.mitre.org/data/definitions/94.html)
- **Tags:** [Path traversal](https://agentprime.io/advisories/tag/path-traversal.md) · [Code injection](https://agentprime.io/advisories/tag/code-injection.md)
- **Published:** 19 Aug 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 19 Aug 2026, 19:16 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `copier` (PyPI): affected `>=9.5.0, <9.15.2`; fixed in `9.15.2`

## Machine-written summary

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

> Copier versions 9.5.0 up to 9.15.1 are affected. A trusted-prefix entry in the trust setting can be bypassed with ".." path segments, so a template that appears to be under a trusted location but actually resolves elsewhere runs its tasks without the trust prompt. An attacker who controls a template URL, such as via a project's answers file during copier update, could execute arbitrary commands. Upgrade to copier 9.15.2, which fixes this.

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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0026, the 18th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:10 UTC: First seen by agentprime
- 31 Oct 2026, 14:10 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-9gmc-jqmh-3rvm)

## Sources

- [GitHub Advisory Database: GHSA-9gmc-jqmh-3rvm](https://github.com/advisories/GHSA-9gmc-jqmh-3rvm)
- [OSV: GHSA-9gmc-jqmh-3rvm](https://osv.dev/vulnerability/GHSA-9gmc-jqmh-3rvm)
- <https://github.com/copier-org/copier/security/advisories/GHSA-9gmc-jqmh-3rvm>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-53951>
- <https://github.com/copier-org/copier>
- <https://github.com/copier-org/copier/releases/tag/v9.15.2>

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-9gmc-jqmh-3rvm>, 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-9gmc-jqmh-3rvm/>. Everything for agents: <https://agentprime.io/llms.txt>.