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A novel adaptation of the ClickFix social engineering technique leverages invisible prompt injection and prompt overdose to compromise AI summarizers embedded in email clients, browser extensions, and productivity platforms.
By hiding malicious instructions in HTML content—using zero-width characters, white-on-white text, tiny fonts, and off-screen positioning—attackers can force automated summarizers to produce step-by-step ransomware deployment guides without ever exposing them to human users.
When such poisoned content is ingested, the repeated hidden payload dominates the model’s context window, steering the generated summary to echo attacker-controlled ClickFix steps.
Recipients, trusting AI summaries more than raw messages, may unknowingly execute the provided commands—effectively turning summarization tools into unwitting ransomware delivery agents.
Invisible Prompt Injection and Prompt Overdose
Invisible prompt injection embeds hidden directives within HTML elements styled to be unreadable by humans but fully processed by AI models.
Techniques include:
- Zero-width characters between visible text
- White-on-white or transparent font colors
- Font sizes set to zero or one pixel
- CSS-based off-screen positioning (e.g.,
position: absolute; left: -9999px)
By repeating the payload dozens of times, the “prompt overdose” strategy ensures that the hidden malicious instructions overpower legitimate content during summarization.
Weaponizing AI Summarizers
- Payload Embedding: Attacker crafts an HTML page or email containing benign visible text plus hidden containers with ransomware delivery steps.
- Directive Steering: A separate invisible “prompt directive” instructs the summarizer to extract and echo only the payload.
- Context Domination: The repeated hidden content saturates the summarizer’s context window, forcing it to output the attacker’s instructions verbatim.
In controlled tests—using both commercial services and custom browser extensions—the generated summaries consistently surfaced Base64-encoded PowerShell commands (e.g., powershell.exe -enc d2hvYW1p) for execution via the Windows Run dialog.
Impact and Risk
This attack vector dramatically lowers the bar for non-technical users to deploy ransomware.
By weaponizing trusted AI assistants, attackers can:
- Scale social engineering across email previews, search snippets, and syndicated content
- Bypass visual inspection and traditional phishing defenses
- Exploit enterprise AI copilots and internal document summarizers
Mitigation Strategies
| Strategy | Description |
|---|---|
| Client-Side Sanitization | Strip or normalize invisible CSS attributes (opacity:0, font-size:0, zero-width chars) |
| Prompt Filtering | Detect and neutralize meta-instructions or excessive repetition before model ingestion |
| Payload Pattern Recognition | Heuristic analysis of Base64 commands and command-line patterns, even if obfuscated |
| Context Window Balancing | De-weight repeated or semantically identical tokens to preserve legitimate content priority |
| UX Safeguards | Warn users when summaries contain hidden-origin instructions or block suspicious outputs |
| Enterprise AI Policy Enforcement | Scan inbound documents for hidden text in email gateways, CMS, and browser extensions |
Looking Ahead
As AI summarizers become ubiquitous, this invisible ClickFix technique may be adopted rapidly by threat actors, potentially packaged into “summarizer exploitation kits.”
Future defenses will require robust hidden-text detection, adversarial prompt engineering, and collaboration between AI developers and security teams to prevent AI-mediated ransomware campaigns.
Organizations and end users should verify that summarization tools sanitize HTML inputs and implement prompt-sanitization controls.
Without these safeguards, AI assistants risk morphing into covert vectors for large-scale social engineering and malware deployment.
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