Apostrophe CMS versions prior to 3.3.1 did not invalidate existing login sessions when disabling a user account or changing the password, creating a situation in which a device compromised by a third party could not be locked out by those means. As a mitigation for older releases the user account in question can be archived (3.x) or moved to the trash (2.x and earlier) which does disable the existing session.

Apostrophe CMS versions between 2.63.0 to 3.3.1 are vulnerable to Stored XSS where an editor uploads an SVG file that contains malicious JavaScript onto the Images module, which triggers XSS once viewed.