Forem is open source software for building communities. Prior to commit a2ab6d4, a maliciously crafted email address could allow an attacker to bypass domain allowlist or denylist restrictions and gain access to invite-only forem deployments. The issue is patched as of `a2ab6d4`. As a workaround, some SMTP servers and email delivery providers may drop or refuse to send maliciously crafted email addresses.
https://github.com/forem/forem/security/advisories/GHSA-3g4h-9h37-mpx6
https://github.com/forem/forem/commit/a2ab6d409d2676eb0711ecbd737192043125b437