CVE-2026-68508: 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:
yaml 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.
Trusted application-owned configuration is not affected in the same way.
Remediation
Hydra 1.3.4 hardens the existing behavior by adding a blacklist of obvious dangerous targets. It is a substantial security improvement, and users remaining on the 1.3 release line should upgrade to 1.3.4 or a newer version.
The unreleased Hydra 1.4 development line uses an allowlist-based instantiation model that fully addresses this vulnerability class. The allowlist must come from trusted application code or another trusted channel, not from the untrusted config being instantiated.
Applications that consume untrusted or semi-trusted config should not pass it directly to hydra.utils.instantiate(). They should validate target values against a trusted allowlist before instantiation.
Other sources
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 resolvetarget() 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 HYDRAINSTANTIATEALLOWLISTOVERRIDE escape hatch. This issue is fixed in version 1.3.4.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/hydra-coreto a version that resolves this vulnerability.Fixed in 1.3.4 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 1.3.4
Event History
Frequently Asked Questions
Which deployments are exposed to exploitation?
Deployments are exposed when an application, library, CLI workflow, or model loader passes untrusted configuration, CLI overrides, or model metadata to hydra.utils.instantiate(). The issue affects Hydra versions prior to 1.3.4.
What does an attacker need to exploit this issue?
An attacker needs a way to control target values or arguments in configuration that reaches hydra.utils.instantiate(). Exploitation also requires a user or workflow to process that untrusted input, as reflected by the user-interaction requirement.
What can successful exploitation do?
Successful exploitation can execute arbitrary code in the consuming process. This can include reading or modifying files and credentials, or terminating the process.
What should teams do if they cannot upgrade immediately?
Do not pass untrusted configuration, CLI overrides, or model metadata into hydra.utils.instantiate(). Version 1.3.4 adds target blocking; its HYDRA_INSTANTIATE_ALLOWLIST_OVERRIDE setting is an explicit escape hatch and should only be used where necessary.