CVE-2026-19861 in JetFormBuilder Plugin
Summary
by MITRE • 09/05/2026
The JetFormBuilder — Dynamic Blocks Form Builder WordPress plugin before 3.6.5.2 does not properly sanitise and escape a form field's value before including it in the HTML notification emails it sends, allowing unauthenticated users to inject arbitrary HTML into messages delivered to administrators and other recipients. Whether injected script executes depends on the recipient's mail client, but the injected markup is rendered regardless.
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Analysis
by VulDB Data Team • 09/07/2026
The JetFormBuilder plugin for WordPress, specifically versions prior to 3.6.5.2, contains a critical input validation flaw that compromises the integrity of email notifications generated by form submissions. This vulnerability stems from an insufficient sanitization and escaping mechanism applied to user-supplied data before it is embedded into HTML-formatted emails. When a visitor submits a form containing dynamic blocks, the plugin processes the field values without adequately filtering out potentially malicious content or encoding special characters that could be interpreted as executable code by email clients. This lack of rigorous input validation allows an unauthenticated attacker to inject arbitrary Hypertext Markup Language (HTML) into the notification messages sent to site administrators and other designated recipients.
From a technical perspective, this flaw represents a classic case of Cross-Site Scripting within an email context, often referred to as Stored XSS if the malicious payload is saved in the database before being rendered during email generation. The vulnerability aligns with CWE-79, which describes Improper Neutralization of Input During Web Page Generation known as 'Cross-site Scripting'. Because the plugin fails to escape HTML entities such as angle brackets and quotes within form field values, any script tags or event handlers embedded in these fields are preserved intact when the email is constructed. This behavior violates fundamental security principles regarding data handling, where all user input must be treated as untrusted until explicitly validated against a strict allowlist of expected formats and characters.
The operational impact of this vulnerability extends beyond simple visual defacement. While the execution of injected scripts depends heavily on the recipient's mail client configuration—many modern clients disable automatic script execution or render emails in plain text by default—the mere presence of rendered markup can be exploited for social engineering attacks. Attackers can craft deceptive email content that mimics legitimate administrative alerts, phishing pages, or malicious links designed to trick administrators into revealing credentials or downloading malware. Furthermore, even if scripts do not execute directly, the ability to inject arbitrary HTML allows attackers to manipulate the visual presentation of emails, potentially obscuring important information or creating confusion regarding the source and authenticity of communications from the website administrator.
This vulnerability is also relevant to the MITRE ATT&CK framework under techniques related to Client-side Injection, specifically T1059 which covers Command and Scripting Interpreter execution via browser-based vectors if scripts are enabled in email clients. It highlights a broader risk associated with WordPress plugins that handle user input for dynamic content generation without implementing robust output encoding strategies. The failure to properly escape data before inclusion in HTML emails creates an attack vector that bypasses traditional web application firewalls, as the malicious payload is delivered through legitimate administrative channels rather than direct website interaction.
To mitigate this vulnerability, administrators must immediately update the JetFormBuilder plugin to version 3.6.5.2 or later, where these sanitization and escaping issues have been addressed by the developers. In addition to updating software, it is advisable to implement strict input validation on all form fields at both the client and server sides, ensuring that only expected data types are accepted. For organizations relying heavily on email notifications for administrative tasks, enabling HTML-free or plain-text-only modes in mail clients can provide an additional layer of defense against rendered script execution. Regular security audits of third-party plugins should also be conducted to identify similar patterns of inadequate input handling across the WordPress ecosystem, ensuring that dynamic content generation processes adhere to secure coding standards and prevent unauthorized code injection through form submissions.