CVE-2026-84647 in Jenkins
Summary
by MITRE • 09/02/2026
In Stapler 2107.v8dfcb_e8ed317 and earlier, except 2088.2093.vd7c3e58008a_6, included in Jenkins 2.579 and earlier, LTS 2.568.2 and earlier, Stapler does not restrict the types of objects that can be instantiated via form data binding to those compatible with the expected field type, allowing attackers with Overall/Read permission to instantiate types related to configuration for which that field type was not intended.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability identified in Stapler versions prior to 2107.v8dfcb_e8ed317 and specifically excluding version 2088.2093.vd7c3e58008a_6, which is integrated into Jenkins releases up to 2.579 and LTS line up to 2.568.2, represents a critical flaw in the framework's form data binding mechanism. Stapler serves as the core web application framework for Jenkins, handling HTTP request processing and object instantiation based on user input. The fundamental technical defect lies in the lack of strict type validation during the deserialization or instantiation process when mapping incoming form parameters to Java objects. Instead of enforcing that the instantiated object matches the expected field type defined in the target class structure, Stapler permits the creation of arbitrary types provided they can be constructed from the supplied data. This permissive behavior creates a significant attack surface for attackers who possess even minimal permissions within the Jenkins environment.
From an operational perspective, this flaw allows authenticated users with Overall/Read permission to exploit the loose binding logic to instantiate classes that are intended only for internal configuration management or administrative tasks but were not designed to be exposed via public-facing forms. By crafting specific HTTP requests containing carefully constructed form data, a low-privileged user can force Stapler to create instances of sensitive configuration objects. These objects often contain methods or properties that interact with the Jenkins core in ways that bypass standard access controls because they are instantiated directly through the framework rather than through proper API endpoints designed for those operations. This effectively elevates the attacker's capabilities beyond their assigned role, potentially leading to unauthorized modification of system settings, exposure of sensitive configuration data, or further exploitation chains depending on how these misconfigured objects interact with other parts of the application.
This vulnerability aligns closely with CWE-20 Improper Input Validation and CWE-94 Improper Control of Generation of Code (Code Injection), as it involves accepting untrusted input that leads to the instantiation of unintended object types. In terms of the MITRE ATT&CK framework, this behavior facilitates privilege escalation by allowing a user to leverage system functionality in an unauthorized manner, mapping to techniques such as T1078 Valid Accounts and potentially T1546 Event Triggered Execution if the instantiated objects trigger specific side effects within the Jenkins runtime. The impact is severe because it undermines the principle of least privilege inherent in Jenkins' security model, allowing read-only users to perform actions that should be restricted to administrators or higher-privileged roles.
Mitigation for this vulnerability requires immediate upgrading of Stapler and Jenkins components to versions where the form data binding logic has been hardened. Specifically, organizations must upgrade to Stapler version 2107.v8dfcb_e8ed317 or later, ensuring that the exclusion case of version 2088.2093.vd7c3e58008a_6 is not inadvertently selected if it lacks the fix. For Jenkins users, this corresponds to upgrading past Jenkins 2.579 and LTS versions beyond 2.568.2. In addition to software updates, administrators should review their security configurations to ensure that Overall/Read permissions are granted only to trusted individuals or service accounts with strict necessity. Implementing additional input validation layers at the application level can provide defense in depth, although reliance on framework-level fixes is paramount for resolving this specific architectural flaw. Regular auditing of user roles and permission assignments further reduces the risk surface by limiting the number of potential attackers who could leverage this vulnerability.