PYSEC-2026-1763

### Summary It's possible to craft a malicious `pdm.lock` file that could allow e.g. an insider or a malicious open source project to appear to depend on a trusted PyPI project, but actually install another project.

### Details Project `foo` can be targeted by creating the project `foo-2` and uploading the file `foo-2-2.tar.gz` to pypi.org. PyPI will see this as project `foo-2` version `2`, while PDM will see this as project `foo` version `2-2`. The version must only be [parseable as a version](https://github.com/frostming/unearth/blob/eca170d9370ac5032f2e497ee9b1b63823d3fe0f/src/unearth/evaluator.py#L215-L229) (and the filename must be a prefix of the project name), but it's [not verified to match the version being installed](https://github.com/pdm-project/pdm/blob/45d1dfa47d4900c14a31b9bb761e4c46eb5c9442/src/pdm/models/candidates.py#L98-L99). (Version `2-2` is also not a valid [normalized version per PEP 440](https://peps.python.org/pep-0440/#post-release-spelling).)

Matching the project name exactly (not just prefix) would fix the issue. The version should also be verified to avoid version downgrade attacks.

### PoC Example `pdm.lock` snippet to appear to depend on `foo` but actually install `foo-2` ``` "foo 2.2.0" = [ url = "https://files.pythonhosted.org/.../foo-2-2.tar.gz ] ```

### Impact When installing dependencies with PDM, what's actually installed could differ from what's listed in `pyproject.toml` (including arbitrary code execution on install). It could also be used for downgrade attacks by only changing the version.