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gstack/browse
Garry Tan 49263b3d10 security(E3): gate GSTACK_SLUG on /welcome path traversal
The /welcome handler interpolates GSTACK_SLUG directly into the filesystem
path used to locate the project-local welcome page. Without validation, a
slug like "../../etc/passwd" would resolve to
~/.gstack/projects/../../etc/passwd/designs/welcome-page-20260331/finalized.html
— classic path traversal.

Not exploitable today: GSTACK_SLUG is set by the gstack CLI at daemon launch,
and an attacker would already need local env-var access to poison it. But
the gate is one regex (^[a-z0-9_-]+$), and a defense-in-depth pass costs us
nothing when the cost of being wrong is arbitrary file read via /welcome.

Fall back to the safe 'unknown' literal when the slug fails validation —
same fallback the code already uses when GSTACK_SLUG is unset. No behavior
change for legitimate slugs (they all match the regex).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-04-21 20:37:37 -07:00
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