CVE-2017-17672 in vBulletin
Summary
by MITRE
In vBulletin through 5.3.x, there is an unauthenticated deserialization vulnerability that leads to arbitrary file deletion and, under certain circumstances, code execution, because of unsafe usage of PHP's unserialize() in vB_Library_Template's cacheTemplates() function, which is a publicly exposed API. This is exploited with the templateidlist parameter to ajax/api/template/cacheTemplates.
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Analysis
by VulDB Data Team • 07/22/2025
The vulnerability identified as CVE-2017-17672 represents a critical security flaw in vBulletin versions up to 5.3.x that stems from improper handling of serialized data within the application's template caching mechanism. This weakness exists in the vB_Library_Template class where the cacheTemplates() function processes user-supplied input without adequate sanitization or validation, creating a pathway for remote attackers to exploit the system through unauthenticated means.
The technical exploitation occurs through the ajax/api/template/cacheTemplates endpoint which accepts a templateidlist parameter that is processed via PHP's unserialize() function. This dangerous usage pattern creates a deserialization vulnerability that allows attackers to craft malicious serialized objects that, when processed, can execute arbitrary code on the server or delete files from the system. The vulnerability is particularly dangerous because it operates through a publicly exposed API endpoint that does not require authentication, making it accessible to any remote attacker.
From an operational perspective, this vulnerability enables attackers to achieve multiple harmful outcomes including arbitrary file deletion and code execution capabilities. The impact extends beyond simple data compromise as attackers can potentially gain full control over the affected server, modify critical application files, or establish persistent access through backdoor installations. The vulnerability's exploitation requires no prior authentication credentials, significantly increasing its attack surface and potential for widespread impact across affected installations.
The weakness aligns with CWE-502 which specifically addresses "Deserialization of Untrusted Data" and represents a classic example of how unsafe deserialization can lead to remote code execution. This vulnerability also maps to ATT&CK technique T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1078 for "Valid Accounts" as attackers can leverage this vulnerability to establish persistent access and execute commands on compromised systems. The attack chain typically involves crafting malicious serialized objects that, when unserialized by the vulnerable application, trigger the desired malicious behavior through the template caching mechanism.
Organizations affected by this vulnerability should immediately implement mitigations including disabling or restricting access to the vulnerable API endpoint, applying the vendor-provided security patches, and implementing network-level restrictions to prevent unauthorized access to the affected functionality. Additionally, comprehensive monitoring should be deployed to detect suspicious activity related to template caching operations and unusual file deletion patterns that may indicate exploitation attempts. The remediation process should include thorough security testing of serialized data handling mechanisms and implementation of proper input validation and sanitization procedures to prevent similar vulnerabilities from emerging in the future.