CVE-2026-65438 in Message Filter for Contact Form 7 Plugin
Summary
by MITRE • 07/28/2026
Unauthenticated Cross Site Scripting (XSS) in Message Filter for Contact Form 7 <= 1.6.3.9 versions.
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Analysis
by VulDB Data Team • 07/28/2026
Cross site scripting vulnerabilities represent one of the most persistent and dangerous threats in web application security landscapes, with unauthenticated variants particularly concerning due to their accessibility to all users without requiring prior authentication or privilege escalation. The specific vulnerability discovered in Contact Form 7 versions 1.6.3.9 and earlier manifests as an unauthenticated cross site scripting flaw within the message filter functionality, creating a direct pathway for malicious actors to inject and execute arbitrary script code in the context of victim browsers. This particular implementation weakness resides in how the application processes and filters user input within contact form messages, failing to properly sanitize or escape potentially malicious content that users might submit through the contact form interface.
The technical nature of this vulnerability stems from insufficient input validation and output encoding mechanisms within the message filter component of the plugin. When users submit contact forms containing specially crafted script tags or malicious payloads, the application processes these inputs through its message filtering system without adequate sanitization measures. This failure allows attackers to inject javascript code that executes in the browser context of legitimate users who view the affected form submissions or related pages. The vulnerability operates at the application layer and can be exploited through various vectors including stored XSS scenarios where malicious scripts are permanently stored on the server and executed whenever the affected content is retrieved, or reflected XSS if the malicious input is immediately reflected back to the user without proper encoding.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the capability to perform session hijacking, steal sensitive cookies, redirect users to malicious websites, or even execute more sophisticated attacks such as credential theft or browser-based malware delivery. Given that contact forms are commonly used across various websites and often contain user information, the potential attack surface is substantial. The unauthenticated nature of this vulnerability means that any visitor to a website running the affected plugin version can exploit it without requiring credentials or privileged access, making it particularly dangerous in environments where multiple users interact with the same vulnerable application. This vulnerability directly maps to CWE-79 which identifies improper neutralization of input during web page generation as a core weakness in web applications.
Security professionals should consider this vulnerability within the broader context of the attack chain described by the MITRE ATT&CK framework, specifically under techniques related to initial access and execution. The exploitation process typically involves crafting malicious payloads that leverage the message filter functionality, which may include injecting javascript through form submissions or manipulating parameters within the contact form processing pipeline. Organizations should prioritize immediate patching of affected installations as a primary mitigation strategy, while also implementing additional protective measures such as content security policies, input validation at multiple layers, and regular security assessments of third-party plugins. The vulnerability demonstrates how seemingly innocuous functionality like message filtering can become a critical security weakness when proper security controls are not implemented. Compliance with industry standards such as OWASP Top Ten and NIST cybersecurity guidelines emphasizes the importance of addressing such vulnerabilities through comprehensive remediation processes including code review, penetration testing, and regular vulnerability scanning to ensure that web applications maintain adequate protection against common exploit vectors like cross site scripting attacks.
The remediation approach must include not only updating to patched versions of Contact Form 7 but also implementing additional defensive measures such as input sanitization, output encoding, and proper validation of all user-supplied content. Organizations should conduct thorough assessments of their web applications to identify similar vulnerabilities in other third-party components and ensure that security controls are consistently applied across all application layers. Regular monitoring and incident response procedures should be established to detect and respond to potential exploitation attempts, while maintaining up-to-date threat intelligence feeds to understand emerging attack patterns targeting similar vulnerabilities.