pnpm: A tarball dependency's manifest `name` escapes node_modules → arbitrary file write/overwrite on install

Summary

When resolving a package, pnpm uses the resolved manifest name as a raw path segment for the isolated-linker import target. A tarball dependency whose package.json name is a scoped path traversal (@x/../../…/<abs path>) is therefore extracted outside node_modules, to an attacker-chosen absolute path, and can overwrite existing files there. Attacker controls the destination, filenames, and contents → arbitrary file write → code execution (e.g. ~/.zshrc, .git/hooks/pre-commit, another package's code). Occurs during pnpm install even with --ignore-scripts (no lifecycle scripts run), defeating that safety.

Same class as the just-patched GHSA-hwx4 (transitive-dependency alias traversal) and GHSA-v23m (stage download manifest name/version traversal), in a sink their fixes did not cover: the isolated-linker import target keyed by the resolved name.

Root cause

• The isolated-linker import target is built with a raw path.join(modules, <resolved name>) in installing/deps-resolver/src/resolvePeers.ts:706, installing/deps-resolver/src/index.ts:614, and deps/graph-builder/src/lockfileToDepGraph.ts:233 — without the safeJoinModulesDir guard used on the symlink/hoisted/bin paths (installing/deps-restorer/src/lockfileToHoistedDepGraph.ts:222). The store location is node_modules/.pnpm/<id>/node_modules/<name>, so a traversal <name> escapes.
• The only resolve-time name gate (resolving/npm-resolver/src/pickPackage.ts:753) rejects only unscoped names containing /, so a scoped @x/../.. passes.

Steps to reproduce

Self-contained PoC (real pnpm@11.9.0; loopback tarball server; escape target is a throwaway temp dir):

npm i pnpm@11.9.0
# host a tarball whose package.json name = "@x/"+"../".repeat(25)+"<abs>/OUTSIDE"; victim depends on the http URL
pnpm install --ignore-scripts

Confirmed output (repro/poc.mjs, exit 0):

escape dir is outside the project        : true
new file implanted outside node_modules  : true
pre-existing file OVERWRITTEN            : true
*** CONFIRMED: a tarball dependency wrote & overwrote files OUTSIDE the project during `pnpm install --ignore-scripts` ***

Remediation

Route the isolated-linker import-target joins (resolvePeers.ts:706, deps-resolver/index.ts:614, lockfileToDepGraph.ts:233) through safeJoinModulesDir (as the hoisted linker already does), and/or enforce validate-npm-package-name on the resolved manifest name (close the scoped-name gap at pickPackage.ts:753) so the import target rejects a traversal name and re-asserts containment before any write.