CVE-2025-55201 in copier
Summary
by MITRE • 08/18/2025
Copier library and CLI app for rendering project templates. Prior to 9.9.1, a safe template can currently read and write arbitrary files because Copier exposes a few pathlib.Path objects in the Jinja context which have unconstrained I/O methods. This effectively renders the security model w.r.t. filesystem access useless. This vulnerability is fixed in 9.9.1.
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Analysis
by VulDB Data Team • 08/18/2025
The vulnerability identified as CVE-2025-55201 affects the copier library and command-line application used for rendering project templates. This issue represents a critical security flaw that undermines the intended filesystem access controls within the application's template rendering system. The vulnerability specifically impacts versions prior to 9.9.1, where the security model designed to restrict filesystem operations becomes completely ineffective due to improper exposure of filesystem objects within the template context.
The technical root cause of this vulnerability lies in how the copier application handles pathlib.Path objects within the Jinja templating context. When template rendering occurs, certain pathlib.Path objects are made accessible to the template environment without proper restrictions on their I/O methods. This exposure allows templates to perform arbitrary file read and write operations through these unconstrained pathlib objects, effectively bypassing all intended security boundaries. The flaw creates a direct pathway for malicious templates to access and manipulate the filesystem beyond what the security model intended to permit.
This vulnerability has significant operational impact as it transforms what should be a controlled template rendering environment into a potential attack vector for unauthorized filesystem access. An attacker could craft malicious templates that read sensitive configuration files, write malicious code to system directories, or manipulate existing files in ways that could compromise system integrity and confidentiality. The security model that was supposed to prevent such arbitrary filesystem access becomes completely useless, rendering the entire template system vulnerable to privilege escalation and data exfiltration attacks.
The fix implemented in version 9.9.1 addresses this issue by properly restricting access to pathlib.Path objects within the Jinja context, ensuring that template rendering operations cannot perform arbitrary file I/O operations. This remediation aligns with security best practices for sandboxed template execution environments and follows the principle of least privilege. Organizations using copier library versions prior to 9.9.1 should urgently upgrade to mitigate this vulnerability. The fix demonstrates proper secure coding practices that prevent information exposure through unconstrained object access, which is consistent with mitigations recommended for CWE-20, CWE-250, and CWE-732 vulnerabilities related to improper privilege management and insecure direct object references. The vulnerability also relates to ATT&CK techniques involving privilege escalation and credential access through potentially compromised software components, emphasizing the need for comprehensive software supply chain security measures.