MaxSite CMS is a widely used content management system that allows individuals and organizations to create and manage digital content. It supports a variety of plugins and themes, enabling users to customize their site according to their needs. Primarily employed by web administrators and developers, MaxSite CMS is designed for ease of use and flexibility, allowing seamless management of blogs, portfolios, or business websites. Its integration capabilities with other applications and services make it a preferred choice for dynamic content-driven websites. The software is popular for its open-source nature, encouraging a collaborative and active developer community. Its focus on providing a user-friendly interface and robust functionalities distinguishes it as an ideal CMS for diverse web projects.
The Remote Code Execution (RCE) vulnerability in MaxSite CMS allows attackers to execute arbitrary code on the server hosting the CMS. The vulnerability is present due to insufficient authentication checks and unsafe handling of user input in the preview-ajax.php endpoint. Attackers can exploit this flaw by crafting a specific request that leverages the PHP eval() function, processing malicious PHP code. This unauthorized code execution can lead to serious security breaches, posing risks to the integrity and confidentiality of data managed by the CMS. Remedial measures have been implemented in version 109.2 to address these concerns, emphasizing enhanced authentication protocols.
The vulnerability resides in the MarkItUp editor's preview AJAX endpoint (preview-ajax.php) of MaxSite CMS. Attackers can construct a POST request targeting the /ajax/ endpoint with specially crafted PHP shortcodes [php]...[/php]. When the request bypasses insufficient authentication mechanisms, the vulnerable endpoint evaluates the code using PHP's eval() function. This oversight allows execution of arbitrary PHP code, leading to potential server compromise. Details like the vulnerable endpoint and the use of PHP eval() illustrate the technical nature of this RCE vulnerability.
Exploiting this vulnerability could allow attackers to execute arbitrary code on the server, potentially leading to full server compromise. Such attacks might enable the installation of malicious software, unauthorized access to sensitive information, or modification of website content. The repercussions could also include data breaches or complete website defacement, adversely affecting the organization's reputation and operational integrity. Furthermore, compromised servers can serve as a launching pad for additional attacks on other networked systems.
REFERENCES
- https://github.com/mbanyamer/CVE-2026-3395-MaxSite-CMS-Unauthenticated-RCE
- https://github.com/rootdirective-sec/CVE-2026-3395-Lab
- https://github.com/maxsite/cms/commit/08937a3c5d672a242d68f53e9fccf8a748820ef3
- https://vuldb.com/?id.348281
- https://www.cyber.gov.au/about-us/view-all-content/alerts-and-advisories/large-scale-exploitation-campaign-targeting-website-content-management-systems-cms
- https://nvd.nist.gov/vuln/detail/CVE-2026-3395
- Upgrade to MaxSite CMS version 109.2 or later to address the vulnerability.
- Implement strict authentication mechanisms for AJAX endpoints to ensure requests are properly authenticated.
- Regularly review and update access permissions to minimize risks stemming from unauthorized code execution.
- Conduct thorough security assessments on current systems to identify and patch other potential vulnerabilities.
- Consider using web application firewall (WAF) solutions to detect and block malicious requests targeting vulnerabilities.
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