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 to them as an encrypted cookie (ex. storing a user provided search query in a cookie) they could then use the generated cookie in place of other more tightly controlled cookies; or if your usage exposed the plaintext version of an encrypted cookie at any point to the user they could theoretically provide encrypted content from your application back to it as an encrypted cookie and force the framework to decrypt it for them. Issue has been fixed in build 468 (v1.0.468).

Reliance on Cookies without validation in OctoberCMS