docs(wasm): say what csp the rendered output needs - #718
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"Self-contained" is true of the markup but not of what a page may load: a frame inherits the embedding page's policy, so the embedder's CSP governs the rendered document, and nothing said what that has to allow. The failures are quiet — under `font-src 'self'` a pdf's `data:` fonts are blocked, and because they carry the code points the text is painted with, every glyph comes out as a replacement box instead of falling back to a system face. Measured across an odt, ods, docx and pdf rendered through the package: `font-src data:`, `img-src data:`, `style-src 'unsafe-inline'` (blocks and, more to the point, hundreds of `style` attributes, which a nonce cannot cover) and `script-src 'unsafe-inline'`. Nothing is fetched from another origin. Closes #710 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XDs5aK3ZGSZsEvqUUwBBXU
Recommending it without qualification was one-sided: it permits `javascript:` urls too, and a document may carry one — odrcore filters a pdf link action down to an allowlist of navigable schemes, but an odt or docx hyperlink is only attribute-escaped. In a `blob:` frame, which is same-origin with the embedder by design, such a link runs with the embedder's origin. The section now says so, and gives the way out for untrusted input: `sandbox="allow-scripts"` without `allow-same-origin`, which keeps the renderer's own scripts working inside the frame and gives up the `contentWindow.odr` API. It also records why hashes or a nonce are not an option here — `embed_shipped_resources`, which would leave no inline script at all, is not bound in the wasm build. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XDs5aK3ZGSZsEvqUUwBBXU
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015d5RcmsA777vwXiuafjx6k
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Closes #710.
wasm/README.mdsaid the rendered html is self-contained and can go straight into ablob:iframe. That is true of the markup, but not of what the page is allowed to load: a frame inherits the embedding page's Content-Security-Policy, so the embedder's policy governs the rendered document — and nothing said what it has to allow.The failures are quiet. Under
font-src 'self'a pdf'sdata:fonts are all blocked, and because a pdf's text is painted with the code points its embedded subset defines, the glyphs do not fall back to a system face — every one comes out as a replacement box. Office formats embed images rather than fonts, which makes it easy to conclude the embed works.Measured, not assumed
Rendered an odt, ods, docx, odp, csv, a standalone image and a pdf through the package and counted what the output carries:
@font-face(data:)<img src="data:"><style>style=attributes<script>about.odtstyle-various-1.docxcomment.odsstyle-various-1.odpstyle-various-1.pdffantastic-landscape.jpgWhich confirms the issue's table, and adds two things it did not name:
style-srccannot be narrowed to a nonce or a hash — most of the styling isstyleattributes, and only'unsafe-inline'(or'unsafe-hashes') covers those.media-srcpointing at wherever the resource was written.Also: nothing is fetched from another origin, so no host ever has to be allow-listed — worth stating, since that is the property the library is meant to have.
The new section gives a working policy, says which part of the output each directive is for, and calls out that a blocked inline script is silent (the layout is css, so the document still looks right while search, editing and the spreadsheet behaviour simply do not run). The
blob:iframe paragraph in Use now points at it.Docs only — no code changes. Independent of #709, which covers the
script-srcthe module itself needs at load time and touches a different part of the file.