CVE-2026-73098 in Juneau
Summary
by MITRE • 11/05/2026
Improper control of dynamically-loaded code vulnerability in Apache Juneau.
When Apache Juneau parses a value into a property of type java.lang.Class (including parameterized forms), the default class swap loaded the named class with initialization enabled, so input naming a class on the application classpath ran that class's static initializer. The impact depends on the classes present in the deployment.
This issue affects Apache Juneau: through 9.2.0.
Users are recommended to upgrade to version 9.2.1, which fixes the issue.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified as Improper Control of Dynamically-Loaded Code within Apache Juneau represents a significant security risk rooted in how the framework handles type conversion and object instantiation during data binding processes. Apache Juneau is a Java library designed to simplify the serialization, deserialization, and transformation of various data formats such as JSON, XML, and CSV into Java objects. The core issue arises when the parser encounters a property defined with the java.lang.Class type or its parameterized variants. In these scenarios, the framework's default behavior involves loading the specified class name using Class.forName() with initialization enabled. This mechanism allows for dynamic class loading at runtime based on user-supplied input values that are mapped to such properties.
From a technical perspective, the flaw lies in the lack of validation or restriction regarding which classes can be loaded dynamically. When an attacker provides a maliciously crafted value corresponding to a Class-type property, they can trigger the execution of static initializers within arbitrary classes present on the application's classpath. Static initializers are blocks of code that run automatically when a class is loaded into memory by the Java Virtual Machine. If these initializers contain side effects such as file system operations, network connections, or other resource-intensive tasks, an attacker can exploit this behavior to cause denial of service conditions or trigger unintended application logic. The severity and specific impact are heavily dependent on the classes available in the deployment environment, meaning that applications with sensitive utility classes or those performing critical initialization routines are at higher risk.
This vulnerability aligns closely with CWE-436, which describes Interpretation Conflict vulnerabilities where different components interpret data differently, leading to security issues, but more specifically it maps to CWE-94 Improper Control of Generation of Code (Code Injection) and CWE-20 Improper Input Validation. In the context of the MITRE ATT&CK framework, this behavior can be associated with Tactic Execution under techniques that involve dynamic code loading or script interpretation, allowing an attacker to influence program flow without direct command execution capabilities in traditional shell terms. The exploitation does not require remote code execution in the sense of injecting arbitrary bytecode but rather leverages legitimate Java mechanisms to perform unauthorized actions through side effects of class initialization.
The operational impact varies based on the specific classes loaded and their static initializer contents. Potential consequences include denial of service due to resource exhaustion, information disclosure if initializers leak sensitive data during startup, or logic bypasses if security checks are circumvented by triggering specific class behaviors before authentication filters execute. Since Apache Juneau is often used in web applications for processing incoming requests, this vulnerability can be triggered remotely via HTTP parameters that map to Class-type fields, making it a viable attack vector against internet-facing services utilizing the library.
To mitigate this risk, users are strongly advised to upgrade Apache Juneau to version 9.2.1 or later, where the issue has been resolved by altering the default behavior of class loading to prevent unintended initialization during property parsing. For applications that cannot immediately upgrade, implementing a custom ClassSwap implementation is recommended. This involves configuring Juneau to use a whitelist approach for allowed classes rather than relying on dynamic resolution from user input. By restricting which classes can be instantiated or loaded based on predefined safe lists, organizations can effectively neutralize the attack surface associated with arbitrary class loading. Additionally, auditing codebases that utilize Class-type properties in data models is essential to identify potential entry points where this vulnerability could be exploited before patches are applied.