copier-org copier up to 9.14.0 YAML File Parser _external_data path traversal

Summaryinfo

A vulnerability marked as critical has been reported in copier-org copier up to 9.14.0. Affected by this issue is the function _external_data of the component YAML File Parser. The manipulation leads to path traversal. This vulnerability is uniquely identified as CVE-2026-34730. Local access is required to approach this attack. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in copier-org copier up to 9.14.0 and classified as problematic. This issue affects the function _external_data of the component YAML File Parser. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-34730 since 03/30/2026. The exploitation is known to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1006 for this issue.

Upgrading to version 9.14.1 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 5413062eb17b73dc885f5e645cdc161e69ef641b is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• copier-org

Name

• copier

Version

• 9.0
• 9.1
• 9.2
• 9.3
• 9.4
• 9.5
• 9.6
• 9.7
• 9.8
• 9.9
• 9.10
• 9.11
• 9.12
• 9.13
• 9.14.0

License

• open-source

Website

• Product: https://github.com/copier-org/copier/

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CPE 2.2info

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