CVE-2026-78374 in T4 Page Builder Extension
Summary
by MITRE • 09/10/2026
Joomla Extension - joomlart.com - Open mail relay via contact AJAX endpoint in T4 Page Builder extension < 2.3.0 - The front-end JSON editor endpoint exposes an action called contact that requires no authentication, no CSRF token, no captcha (when no captcha plugin is enabled) and has no rate limiting. The attacker fully controls the recipient, subject and HTML body, and the mail is sent from the site's configured sender identity (mailfrom/fromname).
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in T4 Page Builder for Joomla versions prior to 2.3.0 represents a critical failure in input validation and access control mechanisms within the extension's AJAX endpoint architecture. Specifically, the front-end JSON editor exposes an action labeled contact that is designed to facilitate email communication directly from the website interface. However, this functionality lacks essential security controls such as authentication requirements, Cross-Site Request Forgery (CSRF) protection tokens, CAPTCHA verification when no external plugin is active, and any form of rate limiting or throttling mechanisms. This combination of missing safeguards creates a direct pathway for abuse by unauthenticated actors who can interact with the endpoint without restriction.
From a technical perspective, the core flaw lies in the unrestricted handling of user-supplied input within the mail sending logic. The attacker gains full control over three critical parameters: the recipient email address, the subject line, and the HTML body content of the outgoing message. Because the system utilizes the site's configured sender identity for the fromname and mailfrom fields, any malicious emails sent through this vector will appear to originate legitimately from the compromised domain. This lack of output validation allows an attacker to craft arbitrary messages that can be delivered to any external or internal mailbox specified by the adversary. The absence of CSRF tokens means that these requests can also be triggered via simple HTML forms on third-party websites, enabling automated attacks without requiring user interaction beyond visiting a malicious page.
The operational impact of this vulnerability is significant and multifaceted. Primarily, it enables open mail relay abuse, allowing attackers to send spam, phishing campaigns, or malware distribution links while masking their true origin behind the victim's domain reputation. This can lead to severe consequences including IP address blacklisting by major email providers, damage to the organization's brand trust, and potential legal liabilities associated with sending unsolicited communications. Furthermore, because the HTML body is fully controllable, attackers could embed malicious scripts or deceptive content designed to exploit recipients who open the emails, thereby extending the attack chain beyond simple spam distribution into active exploitation of end-users. The lack of rate limiting exacerbates this risk by allowing high-volume automated attacks that can overwhelm mail servers or trigger abuse reports against the victim's infrastructure rapidly.
This vulnerability aligns with several well-known industry standards and classification frameworks. It is a classic example of CWE-918, which addresses Server-Side Request Forgery (SSRF) variants involving email injection, although more accurately classified under CWE-74 as Improper Neutralization of Special Elements in Output Used by a Downstream Component, specifically regarding the lack of sanitization on email headers and body content. In terms of access control failures, it maps to CWE-285: Improper Authorization, as the action requires no authentication or authorization checks. Additionally, the ability to send requests from any origin without CSRF tokens corresponds to CWE-352: Cross-Site Request Forgery (CSRF). From an offensive security perspective, this technique is consistent with MITRE ATT&CK tactics related to Initial Access and Command and Control, specifically leveraging legitimate application features for malicious communication.
Mitigation strategies must address both the immediate technical flaws and broader architectural weaknesses. The most effective remediation is to upgrade the T4 Page Builder extension to version 2.3.0 or later, where these security controls have been implemented by the developers. For organizations unable to patch immediately due to compatibility constraints, temporary mitigations should include implementing server-side rate limiting on the specific AJAX endpoint to prevent high-volume abuse. Additionally, administrators can enforce CSRF token validation for all POST requests originating from the front-end editor and ensure that CAPTCHA solutions are enabled or integrated into the contact form workflow. Network-level controls such as configuring mail servers to reject relay attempts from internal IPs unless explicitly authorized by a whitelist of known sender domains can also reduce the effectiveness of this abuse vector, although application-layer fixes remain the primary defense against this specific vulnerability class.