GHSA-85v3-4m8g-hrh6 is a medium-severity (CVSS 4.4) Path Traversal vulnerability in copier. A fix is available for copier — see the affected versions and patch details below.
Copier `_subdirectory` allows template root escape via parent-directory traversal
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-85v3-4m8g-hrh6.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-85v3-4m8g-hrh6 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
copierReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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 | 9.14.1pip install --upgrade 'copier==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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-85v3-4m8g-hrh6 can be triaged on real exposure rather than presence alone.
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 Security finds GHSA-85v3-4m8g-hrh6 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.