Findings from the security review:
- HIGH: private local events leaked in full (title/location/description) to
anyone who could READ a shared or group calendar via GET /api/caldav/events —
the private_event_visibility rule was only enforced in /groups/{id}/combined.
Now enforced in the merge read too, via a shared helper (apply_event_privacy)
so the two paths can't drift.
- HIGH: 'busy' masking was a blacklist that still leaked creator identity,
source-calendar name, recurrence rule and per-event colour. Replaced with a
whitelist (mask_busy_event): only timing/identity/render fields survive.
- MEDIUM: .ics import had no size limit (raw = await file.read()) → memory DoS.
Now capped at 5 MB (413), read before creating any calendar.
- LOW/INFO: profile email now checked for uniqueness + basic format; display
name / username / email length-capped and control-chars stripped.
Deferred (tracked): RRULE expansion cap at the trust boundary, SQLite
PRAGMA foreign_keys + ON DELETE cascade, and JWT-by-user-id + token version.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
