New CSS Attacks Can Break Webmail Defenses to Steal Passwords and Tokens

New research shows content inside an email can escape its message boundary and interfere with the webmail interface. Across attack chains spanning Outlook, Gmail, Fastmail, Proton Mail, Yahoo Mail, and AOL Mail, the techniques can capture passwords, take over third-party accounts, leak tokens, hijack trusted UI actions, and manipulate AI tools that read email. PortSwigger researcher Gareth

Because attacks of this type can go unnoticed for extended periods, the window between initial compromise and detection is often the deciding factor in the eventual impact.

Finally, maintain offline, tested backups and a clear communication plan so that business continuity decisions are made ahead of time rather than under pressure.