## Summary
- Fixes a path traversal vulnerability via symlink when installing
GitHub packages
- Validates symlink targets before creation to ensure they stay within
the extraction directory
- Rejects absolute symlinks and relative paths that would escape the
extraction directory
## Details
When extracting GitHub tarballs, Bun did not validate symlink targets. A
malicious tarball could:
1. Create a symlink pointing outside the extraction directory (e.g.,
`../../../../../../../tmp`)
2. Include a file entry through that symlink path (e.g.,
`symlink-to-tmp/pwned.txt`)
When extracted, the symlink would be created first, then the file would
be written through it, ending up outside the intended package directory
(e.g., `/tmp/pwned.txt`).
### The Fix
Added `isSymlinkTargetSafe()` function that:
1. Rejects absolute symlink targets (starting with `/`)
2. Normalizes the combined path (symlink location + target) and rejects
if the result starts with `..` (would escape)
## Test plan
- [x] Added regression test
`test/cli/install/symlink-path-traversal.test.ts`
- [x] Tests verify relative path traversal symlinks are blocked
- [x] Tests verify absolute symlink targets are blocked
- [x] Tests verify safe relative symlinks within the package still work
- [x] Verified test fails with system bun (vulnerable) and passes with
debug build (fixed)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
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