Attackers Season Spam With a Touch of 'Salt'

The report details a rising email-evasion technique—“hidden text salting”—in which attackers abuse HTML/CSS (opacity, display:none, tiny fonts, matching colors, comments) to insert invisible noise into headers, preheaders, bodies and attachments to bypass parsers and spam filters. Cisco Talos has tracked increased use of this tactic, provided examples of phishing messages using it, and recommends mitigations such as HTML sanitization at ingestion and gateway filters that ignore visually hidden content.