CVE-2026-4963

A weakness has been identified in huggingface smolagents 1.25.0.dev0. This affects the function evaluate_augassign/evaluate_call/evaluate_with of the file src/smolagents/local_python_executor.py of the component Incomplete Fix CVE-2025-9959. This manipulation causes code injection. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

An adversary targets a developer tool, internal AI assistant, or automation platform built on smolagents. They submit a crafted task containing Python code that uses augmented assignment operators or specific call patterns (e.g., __class__.__mro__ traversal via evaluate_augassign/evaluate_call chains) that bypass the incomplete sandbox restrictions. The LocalPythonExecutor evaluates the payload while believing it is safe. The attacker achieves arbitrary code execution on the host, immediately reading HUGGING_FACE_HUB_TOKEN, AWS_SECRET_ACCESS_KEY, or other credentials from environment variables. With cloud credentials in hand, they pivot to exfiltrate models, training data, or customer data stored in connected cloud storage — all triggered through a seemingly legitimate agent task submission.