CVE-2017-17671 in vBulletin
Summary
by MITRE
vBulletin through 5.3.x on Windows allows remote PHP code execution because a require_once call is reachable with an unauthenticated request that can include directory traversal sequences to specify an arbitrary pathname, and because ../ traversal is blocked but ..\ traversal is not blocked. For example, an attacker can make an invalid HTTP request containing PHP code, and then make an index.php?routestring= request with enough instances of ".." to reach an Apache HTTP Server log file.
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Analysis
by VulDB Data Team • 12/31/2019
The vulnerability identified as CVE-2017-17671 represents a critical remote code execution flaw in vBulletin versions 5.3.x running on Windows systems. This security weakness stems from improper input validation within the application's request handling mechanism, specifically affecting how the framework processes directory traversal sequences in URL parameters. The vulnerability exploits a fundamental flaw in path resolution logic where the application fails to properly sanitize user-supplied input that gets processed through a require_once function call.
The technical exploitation mechanism relies on the asymmetric handling of directory traversal sequences in Windows file systems where the application blocks standard forward slash traversal using ../ but fails to block backslash traversal using ..\. This inconsistency creates a pathway for attackers to manipulate the file inclusion process and gain access to arbitrary files on the server. When an attacker submits a malformed HTTP request containing malicious PHP code, they can subsequently leverage the vulnerable routestring parameter to navigate through the directory structure until they reach a location containing a log file or other accessible server component.
This vulnerability directly maps to CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks. The flaw demonstrates how inadequate input validation can lead to arbitrary code execution, a common pattern that aligns with ATT&CK technique T1203 for exploitation through web applications. The impact extends beyond simple code execution as it allows attackers to potentially access sensitive server files, including configuration data, user credentials, and application source code that could reveal additional attack vectors or compromise the entire system.
The operational consequences of this vulnerability are severe for organizations running affected vBulletin installations, as it provides unauthenticated remote code execution capabilities that can be exploited from anywhere on the internet. Attackers can leverage this vulnerability to establish persistent access, escalate privileges, or use the compromised system as a foothold for further network infiltration. The Windows-specific nature of the vulnerability means that organizations running vBulletin on Windows servers are particularly at risk, though the underlying architectural flaw could potentially be exploited on other platforms with similar directory traversal handling.
Mitigation strategies should focus on immediate patching of affected vBulletin installations to version 5.4.0 or later, which contains the necessary fixes for the directory traversal vulnerability. Organizations should also implement network-level protections such as web application firewalls that can detect and block suspicious directory traversal patterns in HTTP requests. Additionally, security teams should conduct comprehensive audits of their vBulletin installations to ensure that no other vulnerable components exist and that proper input validation is implemented throughout the application. Regular security monitoring and log analysis should be enhanced to detect potential exploitation attempts, particularly looking for unusual patterns in routestring parameter usage and access to log files that could indicate attempted exploitation.