Hydra is a framework for elegantly configuring complex applications. Prior to 1.3.4, hydra.utils.instantiate() resolves and calls Python objects selected by configuration through _resolve_target() in hydra/_internal/instantiate/_instantiate2.py, allowing attacker-controlled target values and arguments to choose dangerous callables. A consuming application, library, CLI workflow, or model loader that passes untrusted configuration, CLI overrides, or model metadata into hydra.utils.instantiate() can therefore execute arbitrary code in its own process, including reading or modifying files and credentials or terminating the process. Version 1.3.4 adds target blocking with an explicit HYDRA_INSTANTIATE_ALLOWLIST_OVERRIDE escape hatch. This issue is fixed in version 1.3.4.

A critical arbitrary code execution vulnerability exists in the Hydra configuration framework prior to version 1.3.4. The flaw resides in hydra.utils.instantiate(), which resolves and calls Python objects via _resolve_target() based on configuration values. An attacker who can control configuration inputs, CLI overrides, or model metadata can force the instantiation of dangerous Python callables, leading to arbitrary code execution within the application process. Potential impacts include reading or modifying files, credential theft, and process termination. The vulnerability affects any application, library, CLI workflow, or model loader that passes untrusted input into hydra.utils.instantiate(). Version 1.3.4 mitigates the issue by introducing target blocking with an allowlist mechanism controlled by the HYDRA_INSTANTIATE_ALLOWLIST_OVERRIDE environment variable. Users are strongly advised to upgrade to version 1.3.4 immediately.