CVE-2026-19859 in JetFormBuilder Plugin
Summary
by MITRE • 09/06/2026
The JetFormBuilder WordPress plugin before 3.6.5.2 does not sanitize a request parameter before rendering it as message content, allowing unauthenticated users to execute arbitrary shortcodes registered on the site on any page displaying a form. Escaping is applied to that content before a later shortcode-expansion pass rather than after it, so the escaping can be bypassed.
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Analysis
by VulDB Data Team • 09/06/2026
The JetFormBuilder WordPress plugin, prior to version 3.6.5.2, contains a critical input validation and output encoding flaw that facilitates Cross-Site Scripting attacks through the exploitation of shortcode execution mechanisms. This vulnerability stems from an insufficient sanitization process applied to user-supplied request parameters before they are integrated into message content templates. Specifically, when a form is submitted or rendered, certain input fields allow unauthenticated users to inject arbitrary data that is subsequently processed as part of the plugin's messaging system. The core technical deficiency lies in the order of operations regarding security controls; while escaping mechanisms exist within the codebase, they are applied prior to a subsequent shortcode expansion pass rather than after it. This sequencing error creates a bypass condition where malicious payloads can evade initial sanitization checks by leveraging the dynamic nature of WordPress shortcodes during the rendering phase.
From an operational perspective, this flaw allows unauthenticated attackers to execute arbitrary shortcodes registered on the target website. In the context of WordPress development, shortcodes are powerful macros that allow users to embed complex functionality into posts and pages using simple tags. When an attacker can inject a shortcode payload via the unsanitized parameter, they effectively gain the ability to trigger any function associated with installed plugins or themes that register such shortcodes. This capability significantly expands the attack surface beyond typical cross-site scripting limitations. Instead of merely injecting client-side scripts for cookie theft or session hijacking, the vulnerability enables server-side logic execution depending on which shortcodes are active and how they handle input data.
The impact of this vulnerability is severe because it does not require user authentication to exploit. Any visitor to a page displaying a JetFormBuilder form can manipulate the request parameters to trigger malicious shortcode execution. If the site has plugins installed that register vulnerable shortcodes, an attacker could potentially achieve remote code execution, privilege escalation, or data exfiltration depending on the specific implementation of those shortcodes. Even in scenarios where direct server compromise is not immediately possible, the ability to execute arbitrary logic can lead to significant integrity violations and potential denial-of-service conditions through resource exhaustion attacks triggered by malicious shortcode loops or heavy processing tasks.
This vulnerability aligns with Common Weakness Enumeration (CWE) identifiers such as CWE-79 for Improper Neutralization of Input During Web Page Generation, specifically highlighting the failure in output encoding relative to context, and CWE-829 due to the inclusion of a function from an outside source without proper validation. In terms of the MITRE ATT&CK framework, this behavior maps to techniques involving client-side code injection and potentially command execution if the executed shortcodes interact with system-level functions. The specific mechanism of bypassing escaping through processing order is a classic example of logic flaws in security controls where defensive measures are applied at the wrong stage of the data lifecycle.
To mitigate this vulnerability, site administrators must immediately update the JetFormBuilder plugin to version 3.6.5.2 or later, which addresses these sanitization and ordering issues. Until an upgrade is performed, it is advisable to restrict access to forms that utilize vulnerable parameters if possible, although complete mitigation requires patching the underlying code logic. Developers should ensure that all user inputs are strictly validated against a whitelist of expected values before being processed by any templating or shortcode expansion engines. Furthermore, output encoding must be applied as the final step in the rendering pipeline, ensuring that no further processing occurs after escaping is performed to prevent bypasses through subsequent interpretation layers. Regular security audits and adherence to secure coding standards are essential to preventing similar logic-based vulnerabilities in future development cycles.