CVE-2016-9421 in MyBB
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the Users module in the Admin control panel in MyBB (aka MyBulletinBoard) before 1.8.8 and MyBB Merge System before 1.8.8 might allow remote attackers to inject arbitrary web script or HTML via unspecified vectors.
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Analysis
by VulDB Data Team • 08/08/2020
The CVE-2016-9421 vulnerability represents a critical cross-site scripting flaw discovered in the MyBulletinBoard forum software, specifically within its Users module located in the Admin control panel. This vulnerability affects versions prior to 1.8.8 of both the core MyBB platform and the MyBB Merge System, creating a significant security risk for administrators and users who interact with the administrative interface. The flaw allows remote attackers to inject malicious web scripts or HTML content through unspecified vectors, potentially compromising the entire administrative environment and undermining the security posture of affected installations.
The technical nature of this vulnerability stems from inadequate input validation and output sanitization within the administrative user management functionality. When administrators access the Users module to manage forum members, the application fails to properly sanitize user-supplied data before rendering it in the web interface. This creates an opportunity for attackers to craft malicious payloads that execute within the context of the administrator's browser session, potentially leading to unauthorized actions, data theft, or complete compromise of the administrative privileges. The vulnerability operates at the application layer and specifically targets the administrative control panel where sensitive operations are performed, making it particularly dangerous for organizations relying on MyBB for their online communities.
The operational impact of this vulnerability extends beyond simple script injection, as it provides attackers with a potential foothold for more sophisticated attacks within the administrative environment. An attacker who successfully exploits this vulnerability could potentially escalate privileges, modify user accounts, delete content, or even gain access to sensitive configuration data. The attack vector is particularly concerning because it targets the administrative interface, meaning that successful exploitation would allow attackers to perform actions that could affect the entire forum installation. This vulnerability aligns with CWE-79, which specifically addresses Cross-Site Scripting flaws in web applications, and represents a classic example of how insecure input handling can create persistent security weaknesses in administrative interfaces.
Organizations affected by this vulnerability should immediately implement mitigation strategies including updating to MyBB version 1.8.8 or later, which contains the necessary patches to address the XSS vulnerability. Additional defensive measures should include implementing proper input validation and output encoding mechanisms, establishing network segmentation to limit access to administrative interfaces, and conducting thorough security audits of all administrative modules. Security professionals should also consider implementing web application firewalls to detect and block suspicious script injection attempts, while monitoring for unusual administrative activities that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date software versions and implementing defense-in-depth strategies to protect administrative interfaces from common web application attacks. This case exemplifies ATT&CK technique T1059.007 for Command and Scripting Interpreter, where attackers can leverage XSS vulnerabilities to execute malicious scripts within the browser context of privileged users, and T1548.001 for Abuse of Functionality, where legitimate administrative features are misused to achieve unauthorized access or operations.