CVE-2026-87930 in MaxSite
Summary
by MITRE • 09/09/2026
MaxSite CMS through 109.6 passes the ci_session cookie to unserialize() without class restrictions, allowing unauthenticated attackers to inject PHP objects. Attackers can forge valid session cookies using the hardcoded encryption key to trigger magic methods and corrupt application state or achieve code execution if gadget classes exist.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified in MaxSite CMS versions up to 109.6 represents a critical insecure deserialization flaw rooted in the improper handling of user-supplied input within the session management subsystem. Specifically, the application retrieves the ci_session cookie from HTTP requests and passes it directly to PHP's unserialize function without implementing any form of class whitelisting or restriction mechanisms. This architectural decision creates a direct pathway for unauthenticated attackers to inject arbitrary PHP objects into the application context. The core technical failure lies in the absence of validation checks that would ensure only expected, safe classes are instantiated during the deserialization process, thereby violating fundamental principles of secure coding regarding input sanitization and type safety.
The operational impact of this vulnerability is severe due to the nature of PHP object injection attacks. Attackers can forge valid session cookies by exploiting a hardcoded encryption key present within the application's source code or configuration files. This static credential allows adversaries to construct malicious serialized payloads that, when deserialized by the vulnerable unserialize call, trigger specific magic methods associated with gadget classes available in the environment. These gadgets are typically standard PHP libraries or framework components whose internal logic can be chained together to perform unintended actions. Consequently, an attacker may corrupt application state, escalate privileges within the system context, or achieve remote code execution if suitable exploitable classes are present on the target server.
From a classification perspective, this vulnerability aligns with CWE-502, which denotes Deserialization of Untrusted Data. The attack vector is categorized under ATT&CK technique T1190, Exploit Public-Facing Application, as it leverages exposed web services to execute code injection via manipulated input data. Furthermore, the reliance on a hardcoded secret key for cryptographic operations relates to CWE-798, Use of Hard-coded Credentials, which facilitates the initial stage of payload construction by allowing attackers to bypass integrity checks that would otherwise prevent tampering with session cookies.
Mitigation strategies must address both the immediate technical flaw and broader security hygiene practices. The primary remediation involves replacing direct calls to unserialize with safer alternatives such as json_decode for data exchange formats or implementing a strict class whitelist within custom deserialization wrappers if PHP object serialization is strictly required by legacy code dependencies. Additionally, developers should remove any hardcoded encryption keys from the source code and instead utilize environment variables or secure configuration management systems to store sensitive cryptographic material dynamically at runtime. Regular security audits focusing on input validation and output encoding are essential to prevent similar injection vulnerabilities in future development cycles.