CVE-2018-14724 in Ban List Plugin
Summary
by MITRE
In the Ban List plugin 1.0 for MyBB, any forum user with mod privileges can ban users and input an XSS payload into the ban reason, which is executed on the bans.php page.
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Analysis
by VulDB Data Team • 05/17/2020
The vulnerability identified as CVE-2018-14724 resides within the Ban List plugin version 1.0 for the MyBB forum software platform, representing a critical cross-site scripting flaw that directly impacts user account security and system integrity. This issue specifically affects forum administrators who have mod privileges, creating a dangerous escalation path where privileged users can exploit the system to inject malicious code. The vulnerability stems from inadequate input validation and output sanitization within the plugin's ban reason field, allowing malicious actors to craft payloads that persist within the system and execute when administrators view ban records.
The technical implementation of this vulnerability follows a classic XSS attack pattern where user-controlled data enters the system through the ban reason parameter and is subsequently rendered without proper sanitization. When forum moderators or administrators navigate to the bans.php page, the stored malicious script executes within their browser context, potentially leading to session hijacking, credential theft, or further system compromise. The flaw operates at the application layer and leverages the trust relationship between the administrator and the forum software, making it particularly dangerous as it requires minimal privileges to exploit. This vulnerability directly maps to CWE-79: Cross-site Scripting and aligns with ATT&CK technique T1059.001 for command and scripting interpreter execution.
The operational impact of this vulnerability extends beyond simple data theft, as it creates persistent attack vectors that can be leveraged for ongoing surveillance or system manipulation. An attacker with mod privileges can craft sophisticated payloads that execute in the context of the victim's browser, potentially stealing cookies, redirecting traffic, or even executing additional malicious commands. The persistence of this vulnerability means that once exploited, the malicious code remains active until the ban reason is modified or the page is refreshed, creating a continuous threat surface. The vulnerability affects all users who view the bans.php page, making it particularly dangerous in environments where multiple administrators have access to the plugin functionality. Organizations implementing this plugin face potential data breaches, unauthorized access, and compromised user privacy, with the attack surface expanding to include any user who has the capability to ban others within the forum system.
Mitigation strategies for this vulnerability should focus on immediate input validation and output sanitization measures within the plugin code. The most effective remediation involves implementing strict sanitization of all user inputs before storage and ensuring proper HTML escaping when rendering content in the bans.php page. Security patches should enforce a whitelist approach for acceptable characters in ban reasons and implement Content Security Policy headers to prevent unauthorized script execution. Additionally, access controls should be reviewed to ensure that only authorized administrators can perform ban operations, and audit logging should be enhanced to track all ban-related activities. Organizations should also consider implementing web application firewalls to detect and prevent XSS payloads, while regular security assessments should verify that similar vulnerabilities do not exist in other forum plugins or components. The vulnerability demonstrates the critical importance of input validation in web applications and highlights the need for comprehensive security testing of third-party plugins in forum environments.