Source URL: https://blog.talosintelligence.com/too-salty-to-handle-exposing-cases-of-css-abuse-for-hidden-text-salting/
Source: Cisco Talos Blog
Title: Too salty to handle: Exposing cases of CSS abuse for hidden text salting
Feedly Summary: A simple yet effective tactic, known as hidden text salting, is increasingly used by cybercriminals over the past few months to evade even the most advanced email security solutions, including those powered by machine learning and large language models.
AI Summary and Description: Yes
**Summary**: The text outlines Cisco Talos’s investigation into the security issues related to ‘hidden text salting’ in emails, a technique where attackers use CSS properties to inject obscured malicious content to evade detection by email security systems. This practice poses substantial challenges to both traditional and advanced email security solutions, underscoring the need for enhanced detection and filtering technologies.
**Detailed Description**:
The analysis published by Cisco Talos on the abuse of cascading style sheets (CSS) in emails highlights key insights into the tactics used by threat actors:
– **Hidden Text Salting**: This technique involves embedding irrelevant or malicious content, referred to as “salt,” using CSS properties. Attackers manipulate email content to confuse spam filters and detection algorithms.
– **Prevalence**: Talos reports a significantly higher occurrence of hidden text salting in spam compared to legitimate emails.
– **Detection Challenges**: The method complicates detection by influencing components of email security analysis, where hidden content can evade traditional monitoring systems.
– **Methods of Injection**:
– Attackers deploy invisible text through various CSS properties, including:
– **Text Properties**: Font size set to zero or matching font color to the background.
– **Visibility and Display Properties**: Setting opacity to zero or using the `display: none;` property.
– **Container Control**: Manipulating the size of container elements to include concealed characters.
– **Common Locations for Salt**: Hidden content is frequently found in:
– Preheaders
– Headers
– Attachments
– Email bodies
– **Types of Content Used**: The common types of “salt” identified include:
– Random characters
– Irrelevant paragraphs
– Comments in HTML
– **Potential Impacts on Email Defense Solutions**:
– The stealthy nature of hidden text salting significantly undermines both basic and sophisticated email defenses, particularly those leveraging machine learning.
– Targeting defenses that rely on LLMs for content analysis and detection intensifies the threat landscape.
– **Mitigation Strategies**:
– **Detection**: Employing advanced filtering to specifically identify hidden text in emails is crucial.
– **Filtering**: HTML sanitization at the point of email reception can strip out invisible content before it affects downstream detection processes.
– **Recommendations for Security Practitioners**: Organizations must strengthen their email defense systems against such sophisticated evasion techniques, incorporating machine learning and AI-driven detection mechanisms to recognize and neutralize hidden text threats effectively.
In summary, Cisco Talos’s findings on hidden text salting reveal not only an evolving tactic in email-based attacks but also the critical need for enhanced surveillance and filtering capabilities in email security strategies.