markdown/deck/html_fragment rendered author-influenced content verbatim,
so <script>/<img onerror>/etc. executed on the Daybook origin — self-XSS
against the owner's session, and (post-sharing) unauthenticated via /s/.
Two layers, both in artifacts/views.py:
- Create-time allowlist sanitization via nh3 (maintained ammonia/Rust
sanitizer, not deprecated bleach). Keeps formatting/tables/links/images
(incl. relative /assets URLs) and codehilite markup; drops script, on*
handlers, style, unknown tags, and javascript:/data: URLs. html_full is
deliberately NOT sanitized (documented verbatim escape hatch).
- Serve-time CSP (script-src 'none') for the sanitized kinds, on both
/a/{id} and the unauthenticated /s/{token} route. Being a response
header, it also neutralizes scripts in artifacts stored before this fix.
Not applied to html_full or json/csv (json/csv data is already escaped;
their viewers need their own JS).
Verified live across all kinds; 7 regression tests added. 102 tests pass.
Not addressed (noted in the issue): CSV formula injection,
CSRF_COOKIE_HTTPONLY (moot with XSS closed), nonce CSP for json/csv/full.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
peter
e3c5773e8f