Nathan Esquenazi 39066bc614 security: fix env race, signing key, upload traversal, password hash (#106) ...

* security: fix four audit findings -- env race, signing key, upload traversal, password hash

1. Race condition in os.environ (HIGH): Per-session _agent_lock didn't
   prevent cross-session env writes from interleaving. Added global
   _ENV_LOCK in streaming.py that serializes the entire env save/restore
   block across all sessions.

2. Predictable signing key (MEDIUM): sha256(STATE_DIR) was deterministic.
   Now generates a random 32-byte key on first startup and persists it to
   STATE_DIR/.signing_key (chmod 600). Existing sessions invalidated on
   first restart (acceptable for a security fix).

3. Upload path traversal (MEDIUM): Filename '..' survived the regex
   sanitization (dots are allowed chars). Added explicit rejection of
   dot-only names and safe_resolve_ws() check to verify the resolved
   path stays within the workspace.

4. Weak password hashing (MEDIUM): Replaced bare SHA-256 with PBKDF2-
   SHA256 (600k iterations per OWASP). Uses stdlib hashlib.pbkdf2_hmac,
   no new dependencies. Note: existing passwords must be re-set after
   this change (hash format changed).

Closes #106

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: use random signing key as PBKDF2 salt (replaces predictable STATE_DIR salt)

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

2026-04-04 22:25:08 -07:00

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