CVE-2017-8103 in MyBB
Summary
by MITRE
In MyBB before 1.8.11, the Email MyCode component allows XSS, as demonstrated by an onmouseover event.
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Analysis
by VulDB Data Team • 09/20/2020
The vulnerability identified as CVE-2017-8103 affects MyBB versions prior to 1.8.11 and specifically targets the Email MyCode component within the bulletin board system. This represents a critical cross-site scripting vulnerability that exploits the way the software handles user input in email formatting commands. The flaw allows attackers to inject malicious JavaScript code through email MyCode tags, which can then be executed when other users view the affected content. The vulnerability is particularly concerning because it leverages the onmouseover event handler as demonstrated in the exploit, making it possible to trigger malicious code execution through simple mouse interactions. This type of attack vector demonstrates the dangerous potential for widespread impact within forum environments where users frequently interact with content generated by other community members.
The technical implementation of this vulnerability stems from insufficient input sanitization within MyBB's Email MyCode processing functionality. When users create email links using the MyCode formatting system, the application fails to properly validate and escape special characters in the email addresses or associated attributes. This oversight creates an opening for attackers to inject HTML and JavaScript code that gets rendered in the browser when other users browse the forum. The specific use of onmouseover events in the demonstration indicates that the vulnerability allows for event handler injection, which can lead to various malicious payloads including cookie theft, redirection to malicious sites, or more sophisticated attack vectors. This weakness aligns with CWE-79, which specifically addresses Cross-Site Scripting vulnerabilities in software applications.
The operational impact of CVE-2017-8103 extends beyond simple script execution, as it provides attackers with a potential foothold for more extensive attacks within the forum environment. Since MyBB forums often contain user-generated content and personal information, the ability to inject malicious scripts creates opportunities for session hijacking, data exfiltration, and propagation of attacks to other users. The vulnerability affects not just the immediate forum users but could potentially be exploited to compromise the entire user base, making it particularly dangerous in environments where users trust the community content. Attackers could leverage this vulnerability to steal administrator credentials, manipulate forum content, or redirect users to phishing sites. The vulnerability also aligns with ATT&CK technique T1059.007, which covers the use of script-based commands for execution, and T1566, which involves the delivery of malicious content through social engineering or community platforms.
The remediation for this vulnerability requires immediate patching of MyBB installations to version 1.8.11 or later, which contains the necessary input validation and sanitization fixes. System administrators should ensure that all forum installations are updated promptly to prevent exploitation. Additional mitigations include implementing proper content security policies, monitoring user-generated content for suspicious patterns, and educating users about the risks of clicking on untrusted links within forum environments. Organizations should also consider implementing web application firewalls to detect and block suspicious MyCode patterns. The vulnerability serves as a reminder of the critical importance of proper input validation and output encoding in web applications, particularly in community-driven platforms where user-generated content is prevalent. This incident demonstrates how seemingly minor functionality flaws can create significant security risks, emphasizing the need for comprehensive security testing and validation of all user input processing components within web applications.