CVE-2026-34730
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
Copier before version 9.14.1 has a vulnerability in the _external_data feature that allows a template to load YAML files from template-controlled paths. A malicious template can read local YAML-parseable files accessible to the user and expose their contents in rendered output.
Risk Assessment
The organization may be at risk of sensitive data leakage if users run untrusted Copier templates. Attackers could read configuration files or sensitive data.
Recommendation
Update Copier to version 9.14.1. Avoid using untrusted templates.
Other vulnerabilities in Copier
See all- CVE-2026-62999High
Copier versions 9.5.0 through 9.16.0 contain a vulnerability that allows bypassing the trusted repository prefix. Percent-encoded path segments or separators in a template URL can match a configured trusted prefix before decoding by the HTTP server or Git transport, enabling unsafe template features from a repository outside the trusted prefix after user interaction.
- CVE-2026-53951High
A vulnerability in the Copier library (versions 9.5.0 through 9.15.1) allows bypassing the trust mechanism for templates. The prefix check uses raw `str.startswith` without path normalization, while template fetching normalizes the path, enabling `..` sequences to point to a different, attacker-controlled template. Consequently, code from `tasks`, `migrations`, or `jinja_extensions` executes without a trust prompt.
- CVE-2026-34726Medium
Copier before version 9.14.1 accepts parent-directory traversal (..) in the _subdirectory setting, allowing a template to escape its own directory and render files from the parent directory without the --UNSAFE flag.
Original NVD description (English source)
Copier is a library and CLI app for rendering project templates. Prior to version 9.14.1, Copier's _external_data feature allows a template to load YAML files using template-controlled paths. If untrusted templates are in scope, a malicious template can read attacker-chosen YAML-parseable local files that are accessible to the user running Copier and expose their contents in rendered output. This issue has been patched in version 9.14.1.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS