M-5: safeUrl() blocked javascript:/vbscript:/data:text/html but
allowed data:image/svg+xml, which can execute inline <script>/onload=
when loaded as a document/navigation target despite its "image" MIME
type (defense in depth -- not currently reachable to execution via
this sink, but closing it). Added `data:image/svg+xml` to the existing
DANGEROUS_SCHEME_PREFIXES check, so it's caught after the same
entity-decode/whitespace-strip/lowercase normalization used for the
other blocked schemes (obfuscated variants included). Other
data:image/* types (png/jpeg/gif/webp, ...) remain allowed unchanged.
M-6: HtmlBlock's purifyHtml() allowed <iframe src> through with no
`sandbox` attribute -- a clickjacking/phishing vector even with
DOMPurify already stripping script/on*=. Added a DOMPurify
afterSanitizeAttributes hook, scoped tightly to each purifyHtml() call
(added right before sanitize(), removed in a finally right after) so
it can't leak onto other DOMPurify uses or accumulate duplicates
across repeated calls, that force-sets a restrictive sandbox
(allow-scripts allow-same-origin allow-popups allow-forms -- no
allow-top-navigation) and referrerpolicy=no-referrer on every iframe
that survives sanitization.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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