CVE-2026-23986: Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-21 · updated 2026-06-17
Weakness: CWE-61

Description

Copier is a library and CLI app for rendering project templates. Prior to version 9.11.2, Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use unsafe features like custom Jinja extensions which would require passing the `--UNSAFE,--trust` flag. As it turns out, a safe template can currently write to arbitrary directories outside the destination path by using directory a symlink along with `_preserve_symlinks: true` and a generated directory structure whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc. Version 9.11.2 patches the issue.

Affected products

copier-org copier: before 9.11.2 — fixed in 9.11.2

How to fix

Upgrade to a fixed version: copier-org copier 9.11.2. Check the vendor advisory for mitigations.

References

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