Affected: theskumar python-dotenv

python-dotenv reads key-value pairs from a .env file and can set them as environment variables. Prior to version 1.2.2, `set_key()` and `unset_key()` in python-dotenv follow symbolic links when rewriting `.env` files, allowing a local attacker to overwrite arbitrary files via a crafted symlink when a cross-device rename fallback is triggered. Users should upgrade to v.1.2.2 or, as a workaround, apply the patch manually.

Affected: PyPI: python-dotenv

### Summary

`set_key()` and `unset_key()` in python-dotenv follow symbolic links when rewriting `.env` files, allowing a local attacker to overwrite arbitrary files via a crafted symlink when a cross-device rename fallback is triggered.

### Details

The `rewrite()` context manager in `dotenv/main.py` is used by both `set_key()` and `unset_key()` to safely modify `.env` files. It works by writing to a temporary file (created in the system's default temp directory, typically `/tmp`) and then using `shutil.move()` to replace the original file.

When the `.env` path is a symbolic link and the temp directory resides on a different filesystem than the target (a common configuration on Linux systems using tmpfs for `/tmp`), the following sequence occurs:

1. `shutil.move()` first attempts `os.rename()`, which fails with an `OSError` because atomic renames cannot cross device boundaries. 2. On failure, `shutil.move()` falls back to `shutil.copy2()` followed by `os.unlink()`. 3. `shutil.copy2()` calls `shutil.copyfile()` with `follow_symlinks=True` by default. 4. This causes the content to be written to the **symlink target** rather than replacing the symlink itself.

An attacker who has write access to the directory containing a `.env` file can pre-place a symlink pointing to any file that the application process has write access to. When the application (or a privileged process such as a deploy script, Docker entrypoint, or CI pipeline) calls `set_key()` or `unset_key()`, the sy…

Affected: PyPI: python-dotenv

python-dotenv reads key-value pairs from a .env file and can set them as environment variables. Prior to version 1.2.2, `set_key()` and `unset_key()` in python-dotenv follow symbolic links when rewriting `.env` files, allowing a local attacker to overwrite arbitrary files via a crafted symlink when a cross-device rename fallback is triggered. Users should upgrade to v.1.2.2 or, as a workaround, apply the patch manually.