CVE-2011-5251 in vBulletin
Summary
by MITRE
Open redirect vulnerability in forum/login.php in vBulletin 4.1.3 and earlier allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via the url parameter in a lostpw action.
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Analysis
by VulDB Data Team • 02/24/2019
The vulnerability identified as CVE-2011-5251 represents a critical open redirect flaw within the vBulletin forum software ecosystem, specifically affecting versions 4.1.3 and earlier. This security weakness resides in the forum/login.php script where the application fails to properly validate user input parameters, creating an avenue for malicious actors to manipulate the redirection behavior of authenticated users. The vulnerability manifests when the url parameter is utilized within the lostpw action, allowing attackers to craft malicious links that can redirect users to phishing sites or other unauthorized destinations without proper validation.
From a technical perspective, this vulnerability falls under the category of CWE-601 Open Redirect, which is classified as a weakness in software design where applications fail to validate or sanitize input parameters that control redirection behavior. The flaw occurs because the vBulletin application does not implement proper validation mechanisms to ensure that the url parameter contains only valid, expected values or references within the same domain. This allows attackers to construct URLs with malicious redirect targets that can appear legitimate to end users, particularly when the phishing site mimics the authentic forum interface. The vulnerability specifically exploits the lack of input sanitization in the lost password functionality, which is a common authentication recovery mechanism that typically requires redirecting users to a specified location after password reset operations.
The operational impact of this vulnerability extends far beyond simple redirection, as it enables sophisticated phishing attacks that can compromise user credentials and personal information. Attackers can leverage this weakness to create convincing phishing campaigns by directing users to carefully crafted fake login pages that mirror the legitimate forum interface. When users click on malicious links, they are seamlessly redirected to these fraudulent sites where they unknowingly enter their credentials, which are then captured by the attacker. The vulnerability is particularly dangerous because it operates at the application layer and does not require any special privileges or authentication to exploit, making it accessible to any remote attacker with knowledge of the target forum's structure. This creates a significant risk for forum administrators and their user communities, as compromised credentials can lead to account takeovers, data breaches, and further unauthorized activities within the compromised platform.
Organizations and system administrators should immediately implement mitigations to address this vulnerability by upgrading to patched versions of vBulletin that properly validate the url parameter in the login script. The recommended remediation strategy involves implementing strict input validation that ensures all redirect targets are either internal to the application domain or explicitly approved through a whitelist mechanism. Additionally, security controls should include monitoring for suspicious redirect patterns and implementing proper logging of redirection activities to detect potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques such as T1566 Phishing and T1071.004 Application Layer Protocol: Web Protocols, as it enables attackers to craft malicious web-based phishing campaigns that leverage legitimate forum functionality to redirect users to malicious sites. The mitigation approach should also include user education initiatives to raise awareness about suspicious redirects and the importance of verifying URL authenticity before entering credentials. Organizations should also consider implementing web application firewalls that can detect and block suspicious redirect patterns, along with regular security assessments to identify similar vulnerabilities in other applications within their infrastructure.