CVE-2026-23986 is a symbolic link (symlink) following vulnerability categorized under CWE-61 affecting the copier library and CLI tool, which is used for rendering project templates. Prior to version 9.11.2, copier allowed templates marked as 'safe' to write files only within the destination directory. However, a crafted template can exploit the _preserve_symlinks: true option combined with a symlinked directory structure to escape the intended directory boundary. By creating a symlink pointing outside the destination path and generating files whose rendered paths resolve inside this symlink, the template can cause copier to write files arbitrarily anywhere the user has write permissions. This can lead to overwriting critical system or user files, causing data loss, corruption, or potential disruption of services. The vulnerability does not require elevated privileges or authentication but does require user interaction to run the malicious template. The issue was resolved in copier version 9.11.2 by restricting symlink traversal or sanitizing paths to prevent directory escape. The CVSS 4.0 score of 6.9 reflects medium severity, with local attack vector, low complexity, no privileges required, but user interaction needed, and high impact on integrity and availability.

For European organizations, this vulnerability poses a risk primarily to development and operations environments where copier is used to automate project scaffolding or templating. Successful exploitation can lead to arbitrary file overwrites, potentially corrupting configuration files, source code, or critical system files, resulting in service disruption or data integrity issues. Since the attack requires user interaction to generate a project from a malicious template, the risk is higher in environments where templates are sourced from untrusted or external repositories. The vulnerability could be leveraged in supply chain attacks targeting software development pipelines. Organizations relying on UNIX-like systems (Linux, macOS) are most affected due to symlink support. The impact is amplified in sectors with stringent data integrity requirements such as finance, healthcare, and critical infrastructure. Although no known exploits are reported in the wild yet, the medium severity and ease of exploitation warrant proactive mitigation.

European organizations should immediately upgrade copier to version 9.11.2 or later to apply the official patch. Until upgraded, avoid using templates from untrusted sources, especially those that enable the _preserve_symlinks option. Implement strict code review and validation processes for project templates before use. Employ file system monitoring to detect unexpected file modifications outside designated directories. Use containerized or sandboxed environments for running copier commands to limit potential damage from file overwrites. Educate developers and DevOps teams about the risks of using unsafe templates and the importance of verifying template provenance. Integrate automated scanning tools to detect symlink traversal or directory escape patterns in templates. Finally, maintain regular backups of critical configuration and source files to enable recovery in case of exploitation.