Hydra: hydra.utils.instantiate with untrusted config can lead to code execution

Summary

hydra.utils.instantiate() resolves and calls Python objects from config. If an application passes untrusted config to instantiate(), an attacker who controls _target_ and its arguments can cause arbitrary code execution in the consuming process.

Hydra is not a network service. Exploitation requires a consuming application, library, or user workflow to load attacker-controlled config, CLI overrides, or model metadata and pass it to hydra.utils.instantiate().

Details

Hydra's instantiate API is designed to construct objects and call functions from configuration. For example:

component:
  _target_: package.module.Class
  arg: value

When this config is passed to hydra.utils.instantiate(), Hydra resolves _target_ and calls it with the provided arguments.

This is intended for trusted application configuration. However, if untrusted input controls _target_, the config becomes a callable-selection mechanism. A malicious config can select a callable capable of executing code or commands and provide attacker-controlled arguments.

This issue is the same general class of problem discussed by Unit 42 for downstream AI/ML libraries such as NVIDIA NeMo, where untrusted model metadata was passed into Hydra instantiate:

https://unit42.paloaltonetworks.com/rce-vulnerabilities-in-ai-python-libraries/

Hydra 1.3.4 includes a blacklist for some dangerous _target_ values. That blacklist is defense-in-depth and is not a complete security boundary. The blacklist is not present in the released hydra-core 1.3.3 package, so this issue should not be described as a bypass of a released 1.3.3 blacklist.

Impact

A successful attack can execute code in the process that calls hydra.utils.instantiate(). The impact is limited to the privileges and environment of that process.

Potential impact includes:

• Reading files, credentials, environment variables, or data accessible to the process
• Modifying files, outputs, checkpoints, or application state writable by the process
• Terminating or disrupting the process

Affected Usage

Applications and libraries are affected when they pass untrusted or semi-trusted config, model metadata, CLI overrides, or other externally controlled data to hydra.utils.instantiate() without constraining which targets may be instantiated.