Universal XSS in "Ninja Cookie" browser extension


Level 37
Jan 9, 2020
I found several issues in the extension, one even allowing any website to execute JavaScript code in the context of any other website (Universal XSS).
The Universal XSS vulnerability in Ninja Cookie essentially broke down the boundaries between websites, allowing any website to exploit another. This is already really bad. However, while this particular issue has been resolved, the issue of Ninja Cookie rules being way too powerful hasn’t been addressed yet. As long as you rely on someone else’s rules, be it official Ninja Cookie rules or rules from some third-party, you are putting way too much trust in those. If the rules ever turn malicious, they will compromise your entire browsing.
Read more on linked blog.