Fallow: Jest and Vitest `projects` entries let an analyzed repository make Fallow read files outside the project root

Impact

Fallow reads the Jest and Vitest configs of the repository that it analyzes. A Jest projects entry or a Vitest test.projects entry can name a path. Fallow followed such an entry to a config file and read that file, also when the file was outside the project root. These forms reached outside the root:

• an absolute path or glob, for example /etc/*;
• a path with .. segments, for example ../*;
• a glob with a .* segment, because the glob crate also tests .. against a segment that starts with a literal .;
• a symlink in the project root to a directory above it;
• the extends path of a Vitest inline project;
• a script --config path that is a symlink to a file outside the project root.

Fallow parsed each of these files as a test runner config. Fallow used the content only to credit dependencies, setup files and JSX import sources. Thus unused dependency and unused file findings could change. Fallow did not print the content or send it over the network.

The Fallow threat model states that analysis reads only inside the project root. A crafted repository could make Fallow read files that the user did not expect. Such a read can happen in CI, or when an agent runs Fallow on a cloned repository. The attacker gets changed findings, not the file content.

Versions 2.68.0 to 3.33.1 read outside files through Jest projects. Version 3.33.1 also read them through Vitest test.projects.

Patches

Fixed in 3.34.0. Fallow now resolves each match with symlinks and .. segments removed. Fallow reads the match only when it is inside the project root. A glob whose literal base is outside the project root does not run. The boundary is the project root, so an in-root entry such as <rootDir>/../packages/* still works, also from the config of a workspace package. Fallow also does not read a script --config path that is a symlink to a file outside the project root.

Workarounds

Run Fallow only on repositories that you trust. Before you run Fallow on another repository, check the projects entries of its jest.config.* and vitest.config.* files.