CVE-2026-53951
Copier: trust-prefix bypass via path traversal runs tasks unprompted
Description
Copier is a library and CLI app for rendering project templates. In versions 9.5.0 through 9.15.1, the trust setting's prefix match
(copier/_settings.py) compares the template URL against a trusted prefix with a raw str.startswith and no path normalization, while the URL is normalized when the template is actually fetched (Path.resolve() for local paths; libcurl dot-segment removal for https). A template reference that textually starts with a trusted prefix but contains .. is therefore granted trust yet resolves to a different, attacker-controlled template, whose tasks / migrations / jinja_extensions then run without the --trust prompt — arbitrary command execution. Version 9.15.2 patches the issue.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. 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.
Remediation status
No patched version of the affected component has shipped for CVE-2026-53951 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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 CVE-2026-53951 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 CVE-2026-53951. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-53951 in your dependencies?
O3 detects CVE-2026-53951 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.