CVE-2017-7569 in vBulletin
Summary
by MITRE
In vBulletin before 5.3.0, remote attackers can bypass the CVE-2016-6483 patch and conduct SSRF attacks by leveraging the behavior of the PHP parse_url function, aka VBV-17037.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/26/2020
The vulnerability identified as CVE-2017-7569 represents a critical server-side request forgery flaw in vBulletin versions prior to 5.3.0 that directly undermines the security measures implemented to address CVE-2016-6483. This weakness allows remote attackers to circumvent existing protections by exploiting a specific behavior within PHP's parse_url function, creating a dangerous bypass mechanism that can be leveraged for unauthorized network communications. The vulnerability operates at the application layer and specifically targets the input validation mechanisms that should prevent external requests from being initiated through the vulnerable system. This issue falls under the CWE-918 category of Server-Side Request Forgery, which is classified as a critical security weakness in web applications that can enable attackers to make requests to internal systems that would normally be restricted.
The technical exploitation of this vulnerability relies on the predictable behavior of PHP's parse_url function when processing malformed URLs or specific URL formats that can be manipulated through user input. Attackers can craft malicious inputs that cause the application to parse URLs in unexpected ways, allowing them to bypass the original patch designed to prevent SSRF attacks. The vulnerability demonstrates how a seemingly minor implementation detail in PHP's URL parsing can be weaponized to create significant security risks, particularly when combined with the application's handling of external resource requests. This bypass occurs because the original CVE-2016-6483 patch was insufficiently comprehensive in its validation approach, leaving gaps that can be exploited through careful manipulation of input parameters that are then processed by the parse_url function.
The operational impact of this vulnerability extends beyond simple data exfiltration or service disruption, as it can enable attackers to perform reconnaissance on internal network systems that would normally be isolated from external access. Remote threat actors can leverage this vulnerability to probe internal services, potentially gaining access to sensitive backend systems, databases, or other network resources that should remain protected from external exposure. The attack surface includes potential access to internal APIs, database connections, or other services that might be accessible through the vulnerable application's network stack. This makes the vulnerability particularly dangerous in enterprise environments where vBulletin installations may serve as entry points for broader network infiltration attempts, as the attacker can effectively extend their reach through the application's request handling capabilities.
Organizations should implement immediate mitigations including updating to vBulletin version 5.3.0 or later, which contains the necessary patch to address this specific bypass mechanism. Additional defensive measures include implementing strict input validation for all URL parameters, utilizing network segmentation to isolate vulnerable applications, and deploying web application firewalls that can detect and block suspicious URL patterns. The vulnerability's classification under ATT&CK technique T1071.004 for application layer protocol manipulation highlights the need for comprehensive network monitoring and intrusion detection systems that can identify unusual outbound network requests originating from the vulnerable application. Security teams should also conduct thorough code reviews to identify similar patterns in other applications that might be vulnerable to similar bypass techniques through PHP function behavior exploitation.