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Fuzzing Hugging Face's smolagents sandbox reveals a bug that silently degrades AI agents
A developer fuzzed Hugging Face's smolagents framework and found that its Python sandbox falsely rejected valid code, returning a misleading error about NoneType. The error caused the AI agent to retry the same valid code repeatedly, wasting LLM calls and degrading performance without any crash. The bug, which lies in how the sandbox handles dict spread syntax, was discovered through Sentry event tracking.
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The story highlights a subtle but dangerous class of bugs in AI agent frameworks: silent failures that blame the model instead of the infrastructure, making them hard to detect without observability tools.
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The bug that never crashed: how I fuzzed an AI's own code sandbox and found it lying to its model →
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