Researcher Tests AI Agents Against Prompt Injection Using a Fake GitHub Credential Broker

A developer built a tool called Capbroker, a self-hosted broker that issues capability tickets instead of real API keys to AI agents, then tested how well three AI models resisted prompt injection attacks. A poisoned GitHub issue instructed the agent to call a delete_repository tool, which was never granted in the capability policy. Ollama's llama3.1:8b model was fully fooled, emitting a structured tool call for the unauthorized operation, while Groq's model flagged the missing tool and Gemini explicitly identified the text as an attack. In a second test involving a legitimate collaborator-add capability, Groq's model followed injected instructions and attempted to grant admin access to an attacker-controlled account, which Capbroker's policy layer blocked. The experiment highlights that model-level resistance to prompt injection is inconsistent, and deterministic policy enforcement at the broker layer is essential to prevent credential misuse.
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