CVE-2026-23923 in Zabbix
Summary
by MITRE • 03/24/2026
An unauthenticated attacker can exploit the Frontend 'validate' action to blindly instantiate arbitrary PHP classes. The impact depends on environment setup but appears limited at this time.
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Analysis
by VulDB Data Team • 03/29/2026
This vulnerability resides in the frontend validation mechanism of a web application where the validate action fails to properly authenticate incoming requests. The flaw allows an unauthenticated attacker to manipulate the validation process and trigger instantiation of arbitrary PHP classes through blind object instantiation techniques. The vulnerability stems from insufficient input sanitization and lack of proper access control measures within the frontend validation endpoint. Attackers can leverage this weakness by crafting malicious requests that specify class names to be instantiated, potentially leading to various downstream security implications including remote code execution, denial of service, or information disclosure depending on the application's configuration and available classes.
The technical implementation of this vulnerability involves the exploitation of PHP's object instantiation capabilities through the validate action endpoint. When an attacker sends a crafted request containing class names that should be validated, the application fails to properly verify the legitimacy of these class names before attempting instantiation. This blind instantiation occurs without authentication checks, making the vulnerability particularly dangerous as it can be exploited by anyone with access to the frontend interface. The vulnerability aligns with CWE-470, which addresses the use of insecure deserialization techniques and blind object instantiation, and represents a variant of insecure object instantiation that bypasses normal access control mechanisms. The attack vector operates through the application's failure to implement proper class name validation or whitelisting, allowing arbitrary class loading through the validation process.
The operational impact of this vulnerability varies significantly based on the target environment's configuration and available PHP classes. While the initial impact appears limited, the potential for escalation remains substantial when considering that many web applications contain classes with dangerous capabilities such as file operations, database connections, or system command execution. The vulnerability's severity increases if the application's autoloader is configured to load classes dynamically or if the application contains vulnerable classes that can be exploited through the instantiation process. This weakness creates a potential pathway for attackers to perform privilege escalation, data exfiltration, or system compromise depending on the application's architecture and the classes available in the target environment. The vulnerability can be classified under the ATT&CK technique T1203, which involves exploiting software vulnerabilities to gain access to systems, and may also contribute to broader attack chains involving privilege escalation or lateral movement.
Mitigation strategies for this vulnerability should focus on implementing strict access controls and input validation within the frontend validation endpoint. The most effective approach involves requiring authentication for all validation actions and implementing comprehensive class name validation that either uses whitelisting or strict blacklisting of dangerous classes. Applications should also disable dynamic class loading mechanisms that could be exploited and implement proper object instantiation controls that prevent arbitrary class instantiation. Security measures should include input sanitization, parameter validation, and the implementation of secure coding practices that prevent the use of untrusted input in object creation contexts. Additionally, organizations should conduct regular security assessments to identify and remediate similar vulnerabilities in their codebase, ensuring that all frontend validation mechanisms properly enforce access controls and validate all input parameters to prevent unauthorized object instantiation. The vulnerability represents a clear violation of secure coding principles and should be addressed immediately through proper access control implementation and input validation mechanisms.