Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-10-06T19:18:13.170Z",
  "pubdate": "2026-10-06T19:18:13.170Z",
  "executiveSummary": "The Hydra framework is vulnerable to an arbitrary code execution flaw arising from an insufficient blacklist mechanism within the instantiate() function. This vulnerability, identified as CVE-2026-68508, allows an attacker to bypass security restrictions designed to prevent the execution of arbitrary callables via untrusted configuration files. By leveraging execution wrappers, deserialization primitives, or deferred call logic, an attacker can coerce the application into executing unauthorized code.\nThe vulnerability affects Hydra versions 1.3.4 through 1.3.6 and 1.4.0.dev9. The security impact is critical, as successful exploitation results in full code execution under the privileges of the application process. This flaw effectively turns configuration injection into a remote code execution (RCE) vector. The risk is significant for applications that process configuration data from external or untrusted sources, such as user-submitted payloads or untrusted configuration files. Exploitation requires the attacker to control or influence the configuration passed to the instantiate() method, necessitating a medium level of sophistication to obscure the malicious callable through the identified bypass vectors.",
  "technicalDetails": "The vulnerability resides in the instantiate() logic of the Hydra framework, which is designed to handle complex application configurations by dynamically invoking Python callables defined in configuration files. To mitigate unauthorized execution, Hydra employs a name-based blacklist designed to filter out dangerous functions and classes. However, this blacklist is structurally flawed as it only performs surface-level verification of the 'target' field without accounting for nested execution flows or post-instantiation processing.\nThe root cause is the reliance on name-based filtering that fails to evaluate the semantic intent of the configuration. Because the instantiation process is recursive and capable of processing diverse Python primitives, attackers can mask malicious intent by utilizing intermediate layers. These include execution wrappers such as 'timeit.timeit', which can execute arbitrary code passed as strings; 'pickle.loads', which enables binary deserialization attacks; and various generic dispatch mechanisms or deferred call patterns. By providing a configuration that resolves to a seemingly benign entry point, which then internally triggers the execution of a prohibited callable, an attacker bypasses the blacklisting logic entirely.\nThe attack flow proceeds as follows: First, an attacker identifies an application endpoint that consumes user-provided or externally sourced Hydra configurations. Second, the attacker crafts a configuration dictionary where the 'target' field is set to a wrapper or helper function that passes scrutiny by the blacklist filter. Third, the Hydra 'instantiate()' method processes this configuration. During the recursive expansion of the object graph, the target is resolved to a final, malicious callable. Fourth, because the blacklist check was performed only on the initial target, the framework permits the instantiation. Finally, the application executes the malicious payload with the application's process context, leading to arbitrary code execution.\nThe vulnerability is particularly effective because Hydra’s architecture is inherently designed to resolve complex, nested objects. By chaining aliases or utilizing callable-returning factories, an attacker creates an indirection layer that the current validation logic cannot traverse. The impact is a total compromise of the application's runtime environment, allowing for data exfiltration, lateral movement within the infrastructure, or service disruption, all performed under the guise of legitimate configuration processing."
}