CVE-2025-55201: 
Python vulnerability analysis and mitigation

CVE-2025-55201 affects the Copier library and CLI app (versions < 9.9.1), which is used for rendering project templates. The vulnerability was discovered and disclosed on August 18, 2025. The issue allows a safe template to read and write arbitrary files because Copier exposes pathlib.Path objects in the Jinja context with unconstrained I/O methods, effectively rendering the security model with respect to filesystem access useless (GitHub Advisory).

The vulnerability stems from the exposure of pathlib.Path objects in the Jinja context that have unconstrained I/O methods. This implementation flaw bypasses Copier's intended security model, which should restrict filesystem access through Jinja to only reading files using {% include ... %} from the subtree of the local template clone. The vulnerability has been assigned a CVSS v4.0 base score of 8.5 (High) with the vector string: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N (GitHub Advisory).

The vulnerability enables malicious template authors to perform unauthorized file system operations, including reading sensitive files (such as SSH keys), overwriting existing files, and even deleting files and directories. Attackers could potentially extract secrets from well-known locations, mask them with encoding to reduce detection risk, and exfiltrate the data when users push generated projects to public repositories (GitHub Advisory).

The vulnerability has been fixed in version 9.9.1 of Copier. Users should upgrade to this version or later to address the security issue. No workarounds are available for earlier versions (GitHub Advisory).