CVE-2026-77138 in HTML5 Video Player vs. Powermail Plugin
Summary
by MITRE • 08/25/2026
The extension fails to safely process untrusted client input of an attacker-controlled cookie directly to PHP's unserialize(). A remote, unauthenticated attacker can supply a crafted serialized payload to trigger PHP Object Injection, leading to Remote Code Execution on the TYPO3 server.
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Analysis
by VulDB Data Team • 08/25/2026
This vulnerability represents a critical security flaw within the TYPO3 content management system, specifically affecting an extension that improperly handles user-supplied data from HTTP cookies. The core technical issue stems from the direct invocation of PHP's unserialize function on input derived from client-controlled cookie values without adequate validation or sanitization. In standard web application architecture, cookies are transmitted by the browser to the server with every request and can be easily manipulated by any party capable of intercepting network traffic or accessing the user's local storage. When an extension accepts these values and passes them directly into unserialize(), it creates a vector for PHP Object Injection attacks. This flaw violates fundamental principles of secure coding, particularly the requirement that all external input must be treated as untrusted until proven otherwise through rigorous validation mechanisms.
The operational impact of this vulnerability is severe due to its potential for Remote Code Execution. By crafting a serialized payload containing malicious object instances with specific magic methods or properties, an attacker can exploit the deserialization process to execute arbitrary code within the context of the web server application. This level of access allows the adversary to compromise the integrity and confidentiality of the entire system hosting TYPO3. The attacker does not require authentication, meaning any anonymous user on the internet can attempt this exploitation. Successful exploitation could lead to full system takeover, data exfiltration, defacement of the website, or use of the compromised server as a pivot point for further attacks against internal network resources.
From an industry standards perspective, this vulnerability aligns with CWE-502, which describes Deserialization of Untrusted Data. This category encompasses situations where software reconstructs objects from serialized data without verifying that the source is trustworthy or checking the integrity of the deserialized content. Furthermore, in terms of attack tactics and techniques, this scenario maps directly to MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques such as T1059.004 for PowerShell or T1059.007 for JavaScript, depending on the payload used during exploitation. The initial access vector is classified under T1190, Exploit Public-Facing Application, highlighting the risk associated with exposing vulnerable services to untrusted networks without proper input validation controls in place.
Mitigation strategies must focus on eliminating the direct use of unserialize() with user-controlled data entirely if possible. If deserialization is a functional requirement for the extension, developers should implement strict allowlists that define exactly which classes are permitted during the unserialization process. This can be achieved by utilizing PHP's SPL autoloaders in conjunction with custom serialization handlers or by switching to safer data interchange formats like JSON, which do not support object instantiation and thus neutralize this attack vector. Additionally, implementing input validation routines that reject any serialized strings containing unexpected class names is essential. Security headers such as SameSite cookie attributes should also be configured to mitigate certain types of cross-site request forgery attacks that might facilitate the delivery of malicious cookies, although these do not replace the need for fixing the underlying deserialization flaw. Regular security audits and static code analysis tools capable of detecting unsafe function calls are recommended to prevent similar issues in future development cycles.