Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-53951Copier: trust-prefix bypass via path traversal runs tasks unprompted

High 8.8

In plain English

A high-severity path traversal in copier from copier-org. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.8High

Exploit odds (30 days)0.3%top 82.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	copier	9.15.2	GHSA-9gmc-jqmh-3rvm
PyPI	copier	9.15.2	PYSEC-2026-3818

Affected products (as reported)

Vendor	Product	Versions
copier-org	copier	>= 9.5.0, < 9.15.2

Weakness: CWE-22, CWE-94 · Vector: 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

References

https://github.com/copier-org/copier/security/advisories/GHSA-9gmc-jqmh-3rvm x_refsource_CONFIRM
https://github.com/copier-org/copier/releases/tag/v9.15.2 x_refsource_MISC