Affected: npm: tar

**TITLE**: Race Condition in node-tar Path Reservations via Unicode Sharp-S (ß) Collisions on macOS APFS

**AUTHOR**: Tomás Illuminati

### Details

A race condition vulnerability exists in `node-tar` (v7.5.3) this is to an incomplete handling of Unicode path collisions in the `path-reservations` system. On case-insensitive or normalization-insensitive filesystems (such as macOS APFS, In which it has been tested), the library fails to lock colliding paths (e.g., `ß` and `ss`), allowing them to be processed in parallel. This bypasses the library's internal concurrency safeguards and permits Symlink Poisoning attacks via race conditions. The library uses a `PathReservations` system to ensure that metadata checks and file operations for the same path are serialized. This prevents race conditions where one entry might clobber another concurrently.

```typescript // node-tar/src/path-reservations.ts (Lines 53-62) reserve(paths: string[], fn: Handler) { paths = isWindows ? ['win32 parallelization disabled'] : paths.map(p => { return stripTrailingSlashes( join(normalizeUnicode(p)), // <- THE PROBLEM FOR MacOS FS ).toLowerCase() })

```

In MacOS the ```join(normalizeUnicode(p)), ``` FS confuses ß with ss, but this code does not. For example:

``````bash bash-3.2$ printf "CONTENT_SS\n" > collision_test_ss bash-3.2$ ls collision_test_ss bash-3.2$ printf "CONTENT_ESSZETT\n" > collision_test_ß bash-3.2$ ls -la total 8 drwx…