Update packaged libxml2 (2.9.12 → 2.9.13) and libxslt (1.1.34 → 1.1.35)

Summary

Nokogiri v1.13.2 upgrades two of its packaged dependencies:

• vendored libxml2 from v2.9.12 to v2.9.13
• vendored libxslt from v1.1.34 to v1.1.35

Those library versions address the following upstream CVEs:

• libxslt: CVE-2021-30560 (CVSS 8.8, High severity)
• libxml2: CVE-2022-23308 (Unspecified severity, see more information below)

Those library versions also address numerous other issues including performance
improvements, regression fixes, and bug fixes, as well as memory leaks and other
use-after-free issues that were not assigned CVEs.

Please note that this advisory only applies to the CRuby implementation of
Nokogiri < 1.13.2, and only if the packaged libraries are being used. If you’ve
overridden defaults at installation time to use system libraries instead of
packaged libraries, you should instead pay attention to your distro’s libxml2
and libxslt release announcements.

Mitigation

Upgrade to Nokogiri >= 1.13.2.

Users who are unable to upgrade Nokogiri may also choose a more complicated
mitigation: compile and link an older version Nokogiri against external libraries
libxml2 >= 2.9.13 and libxslt >= 1.1.35, which will also address these same CVEs.

Impact

• libxslt CVE-2021-30560
• CVSS3 score: 8.8 (High)

Fixed by https://gitlab.gnome.org/GNOME/libxslt/-/commit/50f9c9c

All versions of libxslt prior to v1.1.35 are affected.

Applications using untrusted XSL stylesheets to transform XML are vulnerable to
a denial-of-service attack and should be upgraded immediately.

libxml2 CVE-2022-23308

• As of the time this security advisory was published, there is no officially
  published information available about this CVE’s severity. The above NIST link
  does not yet have a published record, and the libxml2 maintainer has declined
  to provide a severity score.
• Fixed by https://gitlab.gnome.org/GNOME/libxml2/-/commit/652dd12
• Further explanation is at https://mail.gnome.org/archives/xml/2022-February/msg00015.html

The upstream commit and the explanation linked above indicate that an application
may be vulnerable to a denial of service, memory disclosure, or code execution if
it parses an untrusted document with parse options DTDVALID set to true, and NOENT
set to false.

An analysis of these parse options:

• While NOENT is off by default for Document, DocumentFragment, Reader, and
  Schema parsing, it is on by default for XSLT (stylesheet) parsing in Nokogiri
  v1.12.0 and later.
• DTDVALID is an option that Nokogiri does not set for any operations, and so
  this CVE applies only to applications setting this option explicitly.

It seems reasonable to assume that any application explicitly setting the parse
option DTDVALID when parsing untrusted documents is vulnerable and should be
upgraded immediately.