Ghosts in the Machine: ASCII Smuggling across Various LLMs – FireTail Blog

Oct 06, 2025 – Alan Fagan – Operationalizing DefenseThe key to catching ASCII Smuggling is monitoring the raw input payload, the exact string the LLM tokenization engine receives, not just the visible text.Ingestion: FireTail continuously records LLM activity logs from all your integrated platforms.Analysis: Our platform analyzes the raw payload data for the specific sequences of Tags Unicode Blocks and other zero-width characters used in smuggling attacks.Alerting: We generate an alert (e.g., “ASCII Smuggling Attempt”) the moment the pattern is detected in the input stream.Response: Security teams can immediately isolate the source (e.g., block the malicious calendar sender) or, more importantly, flag the resulting LLM output for manual review. This prevents the poisoned data from reaching critical systems or other users.
This is a necessary shift in strategy. You can’t rely on the LLM to police itself, and you can’t rely on the UI to show you the full story. Monitoring the raw input stream is the only reliable control point against these application-layer flaws. This is how we are hardening the AI perimeter for our customers.
If you would like to see how FireTail can protect your organization from this and other AI security risks, start a 14-day trial today. Book your onboarding call here to get started.

*** This is a Security Bloggers Network syndicated blog from FireTail – AI and API Security Blog authored by FireTail – AI and API Security Blog. Read the original post at: https://www.firetail.ai/blog/ghosts-in-the-machine-ascii-smuggling-across-various-llms

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AndyC

Andy Curtis is an award-winning security consultant, researcher and public speaker. He has been working in the computer security industry since the early 1990s, having been employed by state and federal government, leading healthcare and banking providers across three continents. He has given talks about computer security for some of the world’s largest companies, worked with law enforcement agencies on investigations into hacking groups, and is a regular voice on TV and radio explaining IT security threats.

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