pnpm: pacquet trust-lockfile install can create dependency symlinks outside the project

Summary

A crafted lockfile alias could reach several install-time filesystem joins. With --trust-lockfile or a frozen lockfile, traversal segments could create links outside the intended project or node_modules boundary. This patch validates dependency names and every virtual-store slot before creating directories, links, bins, or hoisted entries.

Security boundary

• A shared safe-join helper rejects traversal, absolute, platform-specific, and reserved dependency names before filesystem materialization.
• Direct and transitive dependency links, package links, bin destinations, and public/private hoist destinations use the same containment rule.
• Global virtual-store slots validate the complete slot path, including version-derived components, before directory creation.
• Snapshot slots and package names are checked before store initialization and before the current-lockfile fast path, closing the warm-install bypass.
• Rejections preserve ERR_PNPM_INVALID_DEPENDENCY_NAME.

Exploit replay

Before the patch, pacquet install --frozen-lockfile --trust-lockfile accepted a ../../escaped-link dependency key and created a symlink outside the project. With this patch, the same lockfile is rejected before materialization and no outside link is created.

Files changed

• pacquet/crates/package-manager/src/safe_join_modules_dir.rs defines the shared containment rule.
• Install, symlink, bin, hoist, virtual-store, and frozen-lockfile paths call that helper before filesystem materialization.
• The corresponding tests.rs files cover every sink, including warm installs and global virtual-store slots.

Commands run

$ cargo test --locked -p pacquet-package-manager --lib
PASS: 434 tests
$ cargo clippy --locked -p pacquet-package-manager --all-targets -- --deny warnings
PASS
$ cargo fmt --all -- --check
PASS

Validation

• Full pacquet package-manager suite: 434 passed.
• Focused regressions cover direct and transitive aliases, bins, hoists, package names, global virtual-store version traversal, and a poisoned prior-install slot.
• cargo clippy -p pacquet-package-manager --all-targets -- -D warnings: passed.
• cargo fmt --all -- --check and git diff --check: passed.

Compatibility

Valid unscoped and scoped dependency aliases continue to work. The reproduced escape was specific to pacquet, so this branch does not change the TypeScript CLI or the lockfile format.

Written by an agent (Codex, GPT-5).