CVE-2020-19049 in MyBB
Summary
by MITRE • 08/31/2021
Cross Site Scripting (XSS) in MyBB v1.8.20 allows remote attackers to inject arbitrary web script or HTML via the "Description" field found in the "Add New Forum" page by doing an authenticated POST HTTP request to '/Upload/admin/index.php?module=forum-management&action=add'.
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Analysis
by VulDB Data Team • 09/03/2021
This vulnerability represents a critical cross site scripting flaw in MyBB version 1.8.20 that enables authenticated attackers to execute malicious scripts within the context of other users' browsers. The vulnerability specifically targets the administrative interface where forum administrators can create new forums through the "Add New Forum" functionality. The attack vector requires an authenticated user with administrative privileges to make a POST request to the designated administrative endpoint, making it particularly concerning as it leverages existing administrative access rather than requiring initial exploitation of authentication mechanisms.
The technical implementation of this vulnerability occurs through the improper sanitization of user input in the "Description" field of the forum creation form. When administrators enter content into this field, the application fails to adequately validate or escape the input before rendering it in subsequent web pages. This allows attackers who have already gained administrative credentials to inject malicious javascript code, html tags, or other script content that gets executed when other users view the forum descriptions. The vulnerability exists because the application does not implement proper input validation and output encoding mechanisms for administrative form fields.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with a persistent vector for various malicious activities within the MyBB environment. Once exploited, attackers can steal session cookies, redirect users to malicious sites, modify forum content, or even escalate privileges within the application. The vulnerability is particularly dangerous because it operates within the administrative context where attackers have elevated permissions, potentially allowing them to modify forum configurations, delete content, or compromise the entire forum infrastructure. This creates a significant risk for organizations relying on MyBB for community management, as the compromise of administrative accounts can lead to widespread data corruption and unauthorized access.
The vulnerability aligns with CWE-79 which specifically addresses cross site scripting flaws in web applications, and maps to attack techniques in the ATT&CK framework under T1059 for command and script injection. Organizations should implement immediate mitigations including applying the vendor-provided patch for MyBB 1.8.20, implementing proper input validation and output encoding mechanisms, and conducting comprehensive security reviews of administrative interfaces. Additional protective measures include implementing web application firewalls, monitoring for suspicious administrative activities, and ensuring that administrative accounts follow strict security protocols including multi-factor authentication and regular credential rotation. The vulnerability also highlights the importance of proper privilege separation and input sanitization in administrative interfaces to prevent attackers from leveraging legitimate administrative access for malicious purposes.