CVE-2026-78265 in The Events Calendar Plugin
Summary
by MITRE • 08/25/2026
Unauthenticated PHP Object Injection in The Events Calendar <= 6.17.2 versions.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability identified as an unauthenticated PHP object injection flaw within The Events Calendar plugin, affecting versions up to and including 6.17.2, represents a critical security risk that allows remote attackers to execute arbitrary code on the target server without requiring any form of authentication or user interaction. This type of vulnerability stems from the improper handling of serialized data in PHP applications, where an attacker can supply crafted input that is subsequently unserialized by the application logic. In the context of The Events Calendar, this flaw likely resides in a function or endpoint that accepts user-supplied parameters and passes them directly to the php_unserialize() function without adequate validation or sanitization checks against known dangerous classes.
The technical mechanism behind PHP object injection relies on the existence of "magic methods" within instantiated objects, such as __destruct(), __wakeup(), or __toString(). When an attacker provides a serialized string containing references to these magic methods and specific class properties that point to vulnerable functions like file_get_contents() or eval(), the application's unserialization process triggers these methods. This chain reaction allows the execution of arbitrary PHP code with the privileges of the web server user, typically www-data or apache. Because this vulnerability is unauthenticated, it can be exploited by any internet-facing actor who has network access to the WordPress site hosting the plugin, significantly lowering the barrier for entry compared to authenticated vulnerabilities that require valid credentials.
From an operational impact perspective, successful exploitation leads to a complete compromise of the underlying web server and potentially the entire organization's infrastructure if lateral movement is possible. Attackers can use this initial foothold to deface websites, steal sensitive data such as user credentials or database contents, install backdoors for persistent access, or deploy ransomware. The presence of this vulnerability also undermines the integrity and availability guarantees provided by standard web application firewalls that may not inspect serialized payloads effectively unless specifically configured with advanced behavioral analysis rules.
This flaw is categorized under CWE-502, which denotes Deserialization of Untrusted Data, a common weakness in applications that fail to validate or verify data before deserializing it. In terms of the MITRE ATT&CK framework, this vulnerability facilitates initial access through technique T1190, Exploit Public-Facing Application, and enables privilege escalation via command execution techniques such as T1059 if the injected code allows for shell commands to be run on the operating system level. The lack of authentication requirements places it in a high-severity category within most vulnerability scoring systems due to its ease of exploitation and broad attack surface.
Mitigation strategies must prioritize immediate remediation by updating The Events Calendar plugin to version 6.17.3 or later, where this specific deserialization flaw has been patched through stricter input validation and the removal of unsafe unserialization calls. In scenarios where an update cannot be applied immediately due to compatibility concerns with other plugins or custom code, administrators should implement a Web Application Firewall rule that blocks requests containing suspicious serialized payloads or known dangerous class names associated with PHP object injection attacks. Additionally, enabling strict type checking in PHP configurations and disabling the execution of arbitrary functions via disable_functions directives can reduce the blast radius if an exploitation attempt occurs. Regular security audits focusing on input handling and deserialization practices are essential to prevent similar vulnerabilities from being introduced during future development cycles or plugin updates.