CVE-2020-17447 in MyBB
Summary
by MITRE
MyBB before 1.8.24 allows XSS because the visual editor mishandles [align], [size], [quote], and [font] in MyCode.
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Analysis
by VulDB Data Team • 08/10/2020
The vulnerability identified as CVE-2020-17447 represents a cross-site scripting weakness in MyBB forums prior to version 1.8.24, specifically within the visual editor's handling of MyCode formatting tags. This issue arises from insufficient input validation and sanitization mechanisms that fail to properly process certain MyCode elements including align, size, quote, and font tags. The flaw enables malicious actors to inject arbitrary javascript code through these formatting elements, potentially compromising user sessions and executing unauthorized actions on behalf of forum participants.
The technical root cause of this vulnerability stems from improper sanitization of user-supplied content within the MyBB forum software's visual editor component. When users create posts using the visual editor interface, the system processes MyCode tags to format content according to user preferences. However, the implementation fails to adequately validate or escape special characters and javascript payloads embedded within the align, size, quote, and font MyCode parameters. This weakness allows attackers to craft malicious posts containing javascript code within these formatting tags that executes when other users view the affected content. The vulnerability specifically affects the visual editor's MyCode processing pipeline, where user input flows directly into rendered content without proper security filtering.
The operational impact of CVE-2020-17447 extends beyond simple script execution, potentially enabling session hijacking, credential theft, and unauthorized administrative actions within compromised forums. Attackers can exploit this vulnerability to inject malicious scripts that capture user credentials, redirect visitors to phishing sites, or perform actions such as posting spam content or modifying forum settings. The vulnerability affects all forum users who view posts containing malicious MyCode, creating a persistent threat vector that can compromise multiple user sessions over time. Additionally, the visual editor's widespread use within MyBB forums means that even users who do not directly interact with the affected tags can be impacted when viewing forum content.
Security mitigations for this vulnerability involve upgrading to MyBB version 1.8.24 or later, which includes proper input sanitization and validation for MyCode tags. System administrators should also implement additional defensive measures such as content filtering, regular security audits, and user input validation. The vulnerability aligns with CWE-79, which describes cross-site scripting flaws, and can be mapped to ATT&CK technique T1566 for social engineering through malicious content delivery. Organizations should conduct comprehensive security assessments to identify other potential MyCode-related vulnerabilities and implement proper output encoding for all user-generated content. Regular patch management and security monitoring are essential to prevent exploitation of similar vulnerabilities in forum software environments.