Application#sanitize_svg_icon already runs a Loofah scrubber on every
icon upload, but the scrubber class itself was never tracked. Land it
along with tests covering the four shapes that matter:
- <script> elements stripped entirely
- on* event handlers (onload, onclick, …) removed but the carrying
element preserved
- attribute values pointing at javascript:/data: URIs rejected
- benign icons round-trip unchanged
Writing the benign-icon test caught a real bug: the attribute allowlist
holds canonical SVG case (viewBox, preserveAspectRatio, gradientUnits,
…) but safe_attribute? downcases the incoming name before comparing,
so legitimate icons were silently losing those attributes on upload.
Fix by comparing against a precomputed lowercase lookup set; the
constant stays readable as canonical SVG case for documentation.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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