GHSA-85v3-4m8g-hrh6 is a medium-severity (CVSS 4.4) Path Traversal vulnerability in copier. O3 Security confirms whether GHSA-85v3-4m8g-hrh6 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Copier `_subdirectory` allows template root escape via parent-directory traversal
Real-World Exposure
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Description
Summary
Copier's _subdirectory setting is documented as the subdirectory to use as the template root. However, the current implementation accepts parent-directory traversal such as .. and uses it directly when selecting the template root.
As a result, a template can escape its own directory and make Copier render files from the parent directory without --UNSAFE.
Details
The relevant code path is:
- the template defines
_subdirectory - Copier renders that string
template_copy_rootreturnsself.template.local_abspath / subdir- Copier walks that directory as the template root
Relevant code:
- https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/copier/_main.py#L1056-L1062
- https://github.com/copier-org/copier/blob/7aa7021bd73797c982492bac3535515d4484fdb7/copier/_template.py#L504-L513
The effective sink is:
subdir = self._render_string(self.template.subdirectory) or ""
return self.template.local_abspath / subdir
There is no check that the resulting path stays inside the template directory.
The documentation for _subdirectory describes it as:
Subdirectory to use as the template root when generating a project.
and explains it as a way to separate template metadata from template source code:
That description fits values like template or poetry, but not ...
PoC
PoC 1: _subdirectory: .. escapes to the parent directory
mkdir -p root/template dst
echo 'loot' > root/loot.txt
printf '%s\n' '_subdirectory: ..' > root/template/copier.yml
copier copy --overwrite root/template dst
find dst -maxdepth 3 -type f | sort
cat dst/loot.txt
Expected output includes:
dst/loot.txt
dst/template/copier.yml
loot
This shows Copier is rendering from root/ rather than from root/template/.
Impact
If a user runs Copier on an untrusted template, that template can change the effective template root and make Copier render files from outside the intended template directory.
Practical impact:
- template-root escape via
.. - rendering of parent-directory files that were not meant to be part of the template
- possible without
--UNSAFE
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | copier | all versions | 9.14.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for copier. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update copier to 9.14.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-85v3-4m8g-hrh6 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-85v3-4m8g-hrh6 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-85v3-4m8g-hrh6. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-85v3-4m8g-hrh6 in your dependencies?
O3 detects GHSA-85v3-4m8g-hrh6 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.