feat(cruby): patch libxml2 to handle abruptly-closed HTML comments #2294
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Tagging @tehryanx for the cross-over mention from Hackerone. |
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I'm going to wait for feedback on the upstream merge request before merging this. |
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OK, given that Nick has stepped down as a libxml2 maintainer, I'm less confident that the upstream commit will get reviewed or merged, so I'm planning on merging and releasing this in v1.13.0. |
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See guidance provided on abruptly-closed comments here: https://html.spec.whatwg.org/multipage/parsing.html#parse-error-abrupt-closing-of-empty-comment
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What problem is this PR intended to solve?
Hackerone user tehryanx 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:
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.