fix: stop deploy packer from following out-of-root symlinks

[tlowrimore-heroku]

Summary

deploy_to_heroku could read files from outside the folder you asked it to deploy and upload them to Heroku inside your source tarball.

When packaging a workspace, the tool lists files with git ls-files and then calls stat() and readFile() on each one. Both of those follow symlinks. So if a repository contains a symlink that points somewhere outside the selected root (for example, a link named config.txt that actually points to /proc/self/environ), the packer would quietly read that external file and pack its contents into the tarball sent to Heroku. Build code in the repo could then read those bytes.

This means a repository you cloned from someone else could pull files off your machine the moment you deploy it — without any prompt-injection or special access. It was reported through the bug bounty program (W-23510157, CWE-59).

The fix

getSourceFilePaths() and walkDirectory() now:

1. Use lstat() to notice when a path is a symlink.
2. Resolve the symlink's real target with realpath() and check whether it stays inside the workspace root.
3. Skip any symlink whose target escapes the root — its contents are never read or packed.

Symlinks that point to files inside the root are still followed, so normal deploys are unaffected.

Type of Change

Breaking Changes (major semver update)

• Add a ! after your change type to denote a change that breaks current behavior

Feature Additions (minor semver update)

• feat: Introduces a new feature to the codebase

Patch Updates (patch semver update)

• fix: Bug fix
• deps: Dependency upgrade
• revert: Revert a previous commit
• chore: Change that does not affect production code
• refactor: Refactoring existing code without changing behavior
• test: Add/update/remove tests

Testing

Notes:

Added regression tests in src/utils/tarball.spec.ts. They fail against the old code (the out-of-root file lands in the tarball) and pass with this fix. They cover both code paths that walk the workspace: the git ls-files path and the plain directory-walk fallback. A test also confirms that a legitimate symlink pointing inside the root is still included.

Steps:

1. npm test — full suite passes (207 tests).
2. Or: npx mocha src/utils/tarball.spec.ts --grep "symlink handling" to run just the new tests.

Screenshots (if applicable)

N/A

Related Issues

GUS work item: W-23510157

[jdodson]

Approved.

• Visually looked over the PR and lined it up with the description
• Ran a ChatGPT review and it found a thing, it's saying it found a possible edge case in your solution below.

High — Intermediate symlinks bypass containment
tarball.ts:91 checks only when the final path component is a symlink. If Git tracks leak/credentials but leak becomes a symlink to an external directory, lstat("leak/credentials") reports a regular file and its external contents are packed. I reproduced this behavior.

Validate escapesRoot(realRoot, fullPath) for every candidate, not only leaf symlinks, before adding or traversing it.