libxml2 issue: out-of-bounds memory access when parsing an unclosed HTML comment

[Reed Loden <reed () reedloden com>]

(saw this randomly today on Twitter, so figured I'd send it on to make sure
it gets a CVE and actually gets fixed)

https://hackerone.com/reports/57125#activity-384861

"""
This is an out-of-bounds memory access in libxml2. By entering a unclosed
html comment such as <!-- the libxml2 parser didn't stop parsing at the end
of the buffer, causing random memory to be included in the parsed comment
that was returned to ruby. In Shopify, this caused ruby objects from
previous http requests to be disclosed in the rendered page.

Link to the issue in libxml2's bugtracker:
https://bugzilla.gnome.org/show_bug.cgi?id=746048

A patched version of nokogiri (which uses a embedded libxml2) is available
here:
https://github.com/Shopify/nokogiri/compare/1b1fcad8bd64ab70256666c38d2c998e86ade8c0...master

This bug is still not patched upstream, but both libxml2 and nokogiri
developers are aware of the issue.
"""

~reed