Description
Apostrophe Technologies sanitize-html before 2.3.2 does not properly validate the hostnames set by the "allowedIframeHostnames" option when the "allowIframeRelativeUrls" is set to true, which allows attackers to bypass hostname whitelist for iframe element, related using an src value that starts with "/\\example.com".
Remediation
References
https://advisory.checkmarx.net/advisory/CX-2021-4309
https://github.com/apostrophecms/sanitize-html/blob/main/CHANGELOG.md#232-2021-01-26
https://github.com/apostrophecms/sanitize-html/pull/460