How Canaries Stop Prompt Injection Attacks

In memory-safe programming, a stack canary is a known value placed on the stack to detect buffer overflows. If the value changes when a function returns, the program terminates — signaling an attack.

We apply the same principle to LLM agents: insert a small check before and after a sensitive action to verify that the model’s understanding of its task hasn’t changed.

This way, if a task of ‘Summarize emails’ becomes ‘Summarize emails and send them to attacker.com’ – this inconsistency will trigger an alert that will shut the agent’s operations.

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submitted by /u/dvnci1452
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May 19, 2025
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