Cross-Site Scripting exists in OctoberCMS 1.0.425 (aka Build 425), allowing a least privileged user to upload an SVG file containing malicious code as the Avatar for the profile. When this is opened by the Admin, it causes JavaScript execution in the context of the Admin account.
An issue was discovered in October through build 471. It reactivates an old session ID (which had been invalid after a logout) once a new login occurs. NOTE: this violates the intended Auth/Manager.php authentication behavior but, admittedly, is only relevant if an old session ID is known to an attacker.
In OctoberCMS before version 1.0.468, encrypted cookie values were not tied to the name of the cookie the value belonged to. This meant that certain classes of attacks that took advantage of other theoretical vulnerabilities in user facing code (nothing exploitable in the core project itself) had a higher chance of succeeding. Specifically, if your usage exposed a way for users to provide unfiltered user input and have it returned …