fix(security): escape mXSS-detection text fallback in sanitizeHtmlCore - #182
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The double-parse stability check returned raw fragment.textContent when serialize->re-parse output differed. Since every caller assigns the result to an HTML sink (innerHTML/insertAdjacentHTML), entity-smuggled payloads (e.g. <img onerror=...> combined with table foster-parenting to force instability) were handed back as live markup - the mXSS defense itself became the injection sink. The fallback is now HTML-escaped before being returned. Fixes #162 Co-Authored-By: Claude Fable 5 <[email protected]>
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Summary
Fixes #162 (Critical).
The anti-mXSS double-parse in
sanitizeHtmlCorereturned raw, unescapedfragment.textContentwhen the serialize→re-parse output was unstable. Every caller assigns the return value to an HTML sink (innerHTML/insertAdjacentHTMLvia.html(),.append(),bq-html, …), so an attacker could smuggle an entity-encoded payload (<img src=x onerror=...>) plus a construct that forces re-parse instability (<a><table><a>…foster-parenting) and get live markup back — the mXSS defense itself was the injection sink.Fix
The text fallback is now HTML-escaped before being returned (local
escapeHtmlTexthelper insanitize-core.tsto avoid a circular import withsanitize.ts).Verification
<a><table><a><img src=x onerror=alert(1)>; asserts no<img>element materializes when the result is assigned toinnerHTML.<img src=x onerror=alert(1)>(inert text).bun test tests/security.test.ts: 59 pass / 0 fail.tsc --noEmitclean.🤖 Generated with Claude Code