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.