Follow WHATWG guidance for incorrectly-closed HTML comments #2058
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Also see related upstream merge request: https://gitlab.gnome.org/GNOME/libxml2/-/merge_requests/82 |
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this is pre-work related to what I think is an upstream issue in libxml2 regarding parsing comments.
See guidance provided on incorrectly-closed comments here: https://html.spec.whatwg.org/multipage/parsing.html#parse-error-incorrectly-closed-comment
[skip ci]
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Aug 17, 2021
…ed-html-comments feat(cruby): patch libxml2 to handle abruptly-closed HTML comments --- **What problem is this PR intended to solve?** Hackerone user [tehryanx](https://hackerone.com/tehryanx?type=user) reported a method of potentially confusing Loofah sanitizers by taking advantage of the difference between how abruptly-closed comments are handled by libxml2 and how they're handled by WHATWG-guidance-compliant modern browsers. WHATWG advises to treat `<!-->` and `<!--->` as empty comments, but libxml2 today treats these as the _start_ of a comment. https://html.spec.whatwg.org/multipage/parsing.html#parse-error-abrupt-closing-of-empty-comment I've submitted this patch upstream at https://gitlab.gnome.org/GNOME/libxml2/-/merge_requests/124 Similar prior art is for incorrectly-closed comments: - #2058 - https://gitlab.gnome.org/GNOME/libxml2/-/merge_requests/82 **Have you included adequate test coverage?** Yes! **Does this change affect the behavior of either the C or the Java implementations?** This is a behavior change to libxml2/CRuby. Note that nekoHTML/JRuby already follow WHATWG guidance and so JRuby behavior is unchanged.
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This changeset introduces test coverage for both JRuby and CRuby implementations with respect to handling HTML parse errors within comments.
It then introduces a libxml2 patch to comply with the behavior suggested by the WHATWG "Living Standard" doc with respect to incorrectly-closed comments.
It's important to note that WHATWG's guidance is non-normative, but is what's followed by most popular browsers. Further, the difference in behavior between browsers and server-side sanitization done by a library relying on Nokogiri and libxml2 allows opportunity for XSS attacks (https://owasp.org/www-project-top-ten/OWASP_Top_Ten_2017/Top_10-2017_A7-Cross-Site_Scripting_(XSS)).