CVE-2020-4054

In Sanitize (RubyGem sanitize) greater than or equal to 3.0.0 and less than
5.2.1, there is a cross-site scripting vulnerability. When HTML is
sanitized using Sanitize’s “relaxed” config, or a custom config that allows
certain elements, some content in a math or svg element may not be
sanitized correctly even if math and svg are not in the allowlist. You are
likely to be vulnerable to this issue if you use Sanitize’s relaxed config
or a custom config that allows one or more of the following HTML elements:
iframe, math, noembed, noframes, noscript, plaintext, script, style, svg,
xmp. Using carefully crafted input, an attacker may be able to sneak
arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site
scripting) or other undesired behavior when that HTML is rendered in a
browser. This has been fixed in 5.2.1.