Latest / Big Iron Radio / Homelab Brief - Prompt-Injection Defenses: Input and Output Guards

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Homelab Brief - Prompt-Injection Defenses: Input and Output Guards · Big Iron Radio

• 0:02
  Welcome to the Homelab Brief from Big Iron.
• 0:06
  Today, defending self-hosted LLM apps against prompt injection
• 0:11
  and being realistic about what defending even means.
• 0:15
  Quick note, this is an AI voice drawn from a Big Iron guide.
• 0:20
  Links below.
• 0:21
  Start with the hard truth.
• 0:23
  You cannot fully prevent prompt injection.
• 0:26
  The model has no hard boundary between instructions and data to an LLM.
• 0:31
  Text is text.
• 0:31
  So the realistic goal isn't prevention.
• 0:35
  It's blast radius containment.
• 0:38
  Making it so that when injection happens, it doesn't matter much.
• 0:42
  Which means the strongest defense is architectural, not a clever filter.
• 0:47
  Least privilege tools.
• 0:49
  Authorization enforced in your code, never in the prompt.
• 0:53
  Minimal context.
• 0:55
  Sandboxed execution.
• 0:57
  And a human in the loop for anything genuinely dangerous.
• 1:00
  Structure beats string matching every time.
• 1:03
  The design principle to internalize.
• 1:06
  Assume the model is compromised and build so it doesn't matter.
• 1:11
  A model with no dangerous tools and real per-tool authorization can be completely jailbroken and still cause no harm.
• 1:18
  That's the bar not unbreakable prompt, but harmless when broken.
• 1:23
  Two rules that follow directly.
• 1:26
  Never put secrets in the system prompt it can leak, and it is not a security boundary.
• 1:31
  And treat every tool call argument the model produces as untrusted input.
• 1:35
  Validate the ID, check the authorization fields in code, before you act on them.
• 1:42
  Input and output guards scanning for injection attempts on the way in and leaks on the way out are worth adding, but as a second layer.
• 1:50
  They catch the lazy attacks.
• 1:52
  The architecture is what saves you from the clever ones.
• 1:55
  The full defense stacks in the show notes.
• 1:59
  That's your brief.