fix(message): render received external SVG images#13142
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External images are fetched through the image proxy and served with a generic application/octet-stream content type. Browsers sniff raster formats in <img> tags, but they refuse to render SVG unless it is served as image/svg+xml, so SVG logos stayed blank and only the alt text and placeholder were shown. Detect SVG markup in the proxied response and serve it as a sanitised image/svg+xml document. A new SvgSanitizer service strips active content (scripts, event handlers, external/javascript references) and rejects DOCTYPE/entity declarations as XXE defence in depth, even though the <img> context does not execute scripts. Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Joël de Jager <contact@joeldejager.nl>
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Summary
Received emails containing external SVG images did not render. The message showed only the broken-image placeholder and the image's alt text or name. External images are fetched through the image proxy, which served every response as![]()
tag regardless of content type, but they refuse to render SVG unless it is served as
application/octet-stream. Browsers happily sniff raster formats (PNG/JPEG/GIF) out of animage/svg+xml, so SVG logos and graphics stayed blank.Changes
image/svg+xmlcontent type so browsers render it.SvgSanitizerservice that strips active content (scripts, event handlers, external/javascript: references) and rejects DOCTYPE/entity declarations, as defence in depth against XXE and stored XSS even though theThe first screenshot shows the issue; the second screenshot shows it has been resolved.
Assisted-by: Claude:claude-opus-4-8