Discourse is an open source discussion platform. Prior to 3.2.5 and 3.3.0.beta5, the vulnerability allows an attacker to inject iframes from any domain, bypassing the intended restrictions enforced by the allowed_iframes setting. This vulnerability is fixed in 3.2.5 and 3.3.0.beta5.
https://github.com/discourse/discourse/security/advisories/GHSA-4p82-xh38-gq4p
https://github.com/discourse/discourse/commit/76f06f6b1491db6bd09a4017d2c5591431b3b16e
https://github.com/discourse/discourse/commit/188cb58daa833839c54c266ce22db150a3f3a210