CVE-2011-0526 in Forums
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in index.php in Vanilla Forums before 2.0.17 allows remote attackers to inject arbitrary web script or HTML via the Target parameter in a /entry/signin action.
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Analysis
by VulDB Data Team • 02/08/2019
The vulnerability identified as CVE-2011-0526 represents a critical cross-site scripting flaw within the Vanilla Forums platform, specifically affecting versions prior to 2.0.17. This security weakness resides in the index.php file and manifests when processing the Target parameter within the /entry/signin action. The flaw enables remote attackers to execute malicious web scripts or HTML code within the context of other users' browsers, potentially compromising the entire user session and data integrity. The vulnerability operates by failing to properly sanitize or validate user input before rendering it in the application's response, creating an avenue for attackers to inject malicious payloads that execute in the victim's browser environment.
The technical implementation of this XSS vulnerability stems from insufficient input validation and output encoding practices within the Vanilla Forums authentication flow. When the Target parameter is processed during the signin action, the application fails to adequately escape or filter special characters that could be interpreted as HTML or JavaScript code. This weakness allows attackers to craft malicious URLs containing script payloads that get executed when users navigate to the targeted page or when the application redirects users to the specified target. The vulnerability is classified as a reflected XSS attack since the malicious script is reflected back to the user through the application's response, making it particularly dangerous for web applications that rely on user redirection mechanisms for authentication flows.
From an operational perspective, this vulnerability poses significant risks to Vanilla Forums installations and their user communities. Attackers can exploit this flaw to hijack user sessions, steal sensitive authentication tokens, or redirect users to malicious websites for phishing attacks. The impact extends beyond individual user compromise to potentially affect entire forum communities, as the malicious scripts can persist in the application's response until the vulnerability is patched. The vulnerability's exploitation requires minimal technical skill and can be automated, making it particularly dangerous for widespread deployment. According to CWE classification, this represents a CWE-79: Improper Neutralization of Input During Web Page Generation, which is a fundamental weakness in web application security that allows for arbitrary code execution in user browsers.
The attack surface for this vulnerability encompasses any Vanilla Forums installation running versions earlier than 2.0.17 that utilize the entry/signin functionality with user-provided Target parameters. This includes not only the direct authentication flow but also any application components that might process or redirect based on user input. The vulnerability is particularly concerning because it occurs during the authentication process, a critical phase where users are most likely to trust the application's behavior. Security frameworks such as the ATT&CK matrix classify this vulnerability under the T1531: Account Access Token Manipulation technique, as it can lead to unauthorized access to user accounts and session hijacking. Organizations running vulnerable versions of Vanilla Forums should immediately implement mitigations including input validation, output encoding, and proper parameter sanitization to prevent exploitation.
Mitigation strategies for CVE-2011-0526 should prioritize immediate patching to version 2.0.17 or later, which contains the necessary security fixes. Additionally, administrators should implement proper input validation and output encoding mechanisms that prevent special characters from being interpreted as executable code. The implementation of Content Security Policy headers can provide an additional layer of protection by restricting the sources from which scripts can be loaded. Regular security audits and penetration testing should be conducted to identify similar vulnerabilities in other application components. Organizations should also consider implementing web application firewalls to detect and block malicious payloads attempting to exploit this vulnerability. The vulnerability highlights the importance of proper security coding practices and input validation in web applications, particularly those handling user authentication and redirection mechanisms.