CVE-2026-106442: Hydra instantiate target blacklist bypasses permit code execution
Summary
Hydra's instantiate() API resolves and invokes Python callables named by the target field in configuration. The target blacklist introduced for CVE-2026-68508 was incomplete.
Representative bypasses included execution wrappers such as timeit.timeit, executable deserialization through pickle.loads, and generic dispatch or wrapper targets that obscured the effective callable. Target aliases, callable-returning helpers, and deferred dispatch could similarly bypass name-based checks.
An attacker who can cause an application to instantiate an untrusted Hydra configuration can use these gaps to execute code with the application's privileges.
Fix
Hydra 1.3.6 expands and hardens the blacklist used by the 1.3 compatibility line. It blocks the reported execution and deserialization surfaces, checks canonical callable identities and aliases, mediates callable results, and blocks generic dispatch and wrapper targets that bypass immediate target checks.
The Hydra 1.3 blacklist is a best-effort, defense-in-depth measure. It is not a complete security boundary and does not make untrusted configuration safe to instantiate.
Hydra 1.4.0.dev9 applies the same hardening and introduces the execution whitelist as the recommended primary security boundary. When a whitelist is supplied, targets are rejected unless trusted Python code authorizes them. If no whitelist is supplied, Hydra preserves legacy behavior with a deprecation warning and the blacklist as a best-effort compatibility fallback. Targets that permit configuration to select or supply executable behavior remain non-whitelistable.
Remediation
Upgrade to Hydra 1.3.6, or to Hydra 1.4.0.dev9 or later when testing the 1.4 prerelease line.
On Hydra 1.3, do not instantiate configuration from untrusted sources. On Hydra 1.4 and later, constrain untrusted configuration with a narrow execution whitelist supplied by trusted Python code.
For Hydra 1.4 execution-whitelist configuration, see: https://hydra.cc/docs/advanced/executionwhitelist/
Other sources
Hydra is a framework for elegantly configuring complex applications. From 1.3.4 until 1.3.6 and 1.4.0.dev9, the instantiate() target blacklist introduced for CVE-2026-68508 incompletely checks the effective callable selected by the target field. Execution wrappers such as timeit.timeit, executable deserialization through pickle.loads, aliases, callable-returning helpers, generic dispatch, and deferred calls can obscure or defer the effective target and bypass name-based authorization. An attacker who causes an application to instantiate untrusted Hydra configuration can use these gaps to execute code with the application's privileges. This issue is fixed in versions 1.3.6 and 1.4.0.dev9.
— 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 1.4.0.dev9 - Upgrade
Upgrade
pip/hydra-coreto a version that resolves this vulnerability.Fixed in 1.3.6 - Upgrade
Upgrade
Hydrato a version that resolves this vulnerability.Fixed in 1.3.6 - Upgrade
Upgrade
Hydrato a version that resolves this vulnerability.Fixed in 1.4.0.dev9 - Configuration
On Hydra 1.4 and later, constrain untrusted configuration with a narrow execution whitelist supplied by trusted Python code.
Hydra instantiate() execution whitelist = narrow whitelist supplied by trusted Python code - Compensating control
On Hydra 1.3, do not instantiate configuration from untrusted sources.
Event History
Frequently Asked Questions
Which deployments are exposed?
Applications that call Hydra's instantiate() on untrusted configuration are exposed. Successful exploitation runs code with the privileges of the application performing the instantiation.
What does an attacker need to do to exploit this issue?
The attacker must be able to cause the application to instantiate untrusted Hydra configuration. They can use wrappers, aliases, callable-returning helpers, generic dispatch, deferred calls, or pickle-based deserialization to obscure or defer the effective callable.
Which versions contain the fix?
The issue is fixed in Hydra versions 1.3.6 and 1.4.0.dev9.