Harden: reject clipboard-paste HTML on the message field - #216
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Baskarayelu merged 1 commit intoAug 28, 2026
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No paste-sanitization utility existed anywhere in the app. Add lib/sanitizePaste.ts: getPlainTextFromPaste() reads only the text/plain clipboard entry, never text/html, and createPlainTextPasteHandler() is a drop-in onPaste handler that prevents the default paste and splices the plain text in at the current selection instead, so HTML from a rich-text clipboard source can never reach a plain-text field's value.
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Note on scope
This app has no message/rich-text field yet. Rather than skip the issue, I added the reusable sanitization utility a message field would use, so it's ready to wire in.
Summary
No paste-sanitization existed anywhere in the codebase -- a plain-text field's default paste behavior carries whatever MIME types the clipboard has, including `text/html` from a rich-text source (an email client, a web page), which can inject markup a plain-text field was never meant to hold.
Change
`lib/sanitizePaste.ts`:
Tests
`lib/sanitizePaste.test.ts`: `getPlainTextFromPaste` returns the plain-text payload, never reads `text/html`, handles missing clipboard data; the handler prevents default, splices at an empty selection, and replaces a non-empty selection.
`npx vitest run lib/sanitizePaste.test.ts`: 6 passed. `npx tsc --noEmit` / `npx eslint` on changed files: clean.
Related to #111