CVE-2026-78531 in Jacqueline Plugin
Summary
by MITRE • 10/10/2026
Unauthenticated PHP Object Injection in Jacqueline <= 2.22 versions.
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Analysis
by VulDB Data Team • 10/10/2026
The vulnerability identified as an unauthenticated PHP object injection flaw within the Jacqueline content management system prior to version 2.23 represents a critical security risk that allows attackers to execute arbitrary code on the target server without requiring valid credentials. This type of vulnerability stems from the improper handling of user-supplied input during the deserialization process, where data is converted back into PHP objects with insufficient validation or sanitization checks. In many modern web applications and CMS platforms like Jacqueline, serialization is often used for caching sessions, storing configuration states, or passing complex data structures between different parts of the application. When an attacker can control the serialized string that gets passed to a function such as unserialize(), they can manipulate the object properties to trigger unintended side effects within the PHP runtime environment.
The technical root cause lies in the presence of magic methods, specifically __wakeup() or other destructors and constructors, which are automatically invoked when an object is deserialized. If these methods interact with external resources like file systems, databases, or network connections based on properties that can be controlled by an attacker, it creates a chain of execution known as a gadget chain. By crafting a specific serialized payload containing malicious objects from the application's available classes, an attacker can force the PHP interpreter to execute arbitrary functions. This bypasses standard authentication mechanisms because the vulnerability is triggered during the initial processing of HTTP requests or session data before any user identity verification takes place. The lack of input validation means that even unauthenticated visitors can inject payloads directly into request parameters, cookies, or headers depending on how the application processes incoming data streams.
From an operational perspective, the impact of this vulnerability is severe and potentially catastrophic for system integrity. Successful exploitation allows remote code execution with the privileges of the web server process, which typically runs under a user account such as www-data or nginx. This grants attackers full control over the underlying operating system, enabling them to read sensitive configuration files containing database credentials, modify website content, install backdoors, pivot into internal network segments, and exfiltrate data from connected databases. The unauthenticated nature of the exploit significantly lowers the barrier for entry, allowing automated scanning tools and opportunistic attackers to compromise vulnerable instances at scale without needing to discover valid usernames or passwords first. This leads to widespread defacement, service disruption through denial-of-service attacks, and potential compliance violations due to unauthorized access to personal data stored within the CMS.
Mitigation strategies must prioritize immediate patching as the primary defense vector. Administrators running Jacqueline versions 2.22 and below should upgrade immediately to version 2.23 or later where this deserialization flaw has been remediated through stricter input validation and safe serialization practices that prevent arbitrary object instantiation. For environments where upgrading is not immediately feasible, implementing a Web Application Firewall with rules capable of detecting malicious serialized payloads can provide temporary protection by blocking requests containing known gadget chain signatures. Additionally, enforcing strict Content Security Policies and disabling dangerous PHP functions such as unserialize() in contexts where they are not strictly necessary reduces the attack surface. Organizations should also conduct regular vulnerability assessments focusing on input validation across all entry points to ensure that no user-controlled data is directly passed into deserialization routines without rigorous type checking and allow-listing of expected object classes.