CVE-2006-4706 in MyBB
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in inc/functions_post.php in MyBB (aka MyBulletinBoard) 1.1.7 allows remote attackers to inject arbitrary web script or HTML via a url BBCode tag that contains a javascript URI with an SGML numeric character reference and an embedded space, as demonstrated using "java& #115;cript," a different vulnerability than CVE-2006-3761.
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Analysis
by VulDB Data Team • 04/30/2019
The vulnerability identified as CVE-2006-4706 represents a cross-site scripting flaw within the MyBB bulletin board software version 1.1.7, specifically affecting the inc/functions_post.php file. This security weakness enables remote attackers to execute malicious scripts within the context of other users' browsers through carefully crafted input. The vulnerability exploits the processing of BBCode tags, particularly the url tag, which is commonly used for creating hyperlinks within forum posts. The attack vector involves embedding javascript URIs within the url BBCode tag, leveraging SGML numeric character references to bypass standard input sanitization mechanisms.
The technical implementation of this vulnerability demonstrates a sophisticated evasion technique that combines multiple encoding methods to circumvent security filters. Attackers exploit the specific parsing behavior of MyBB's BBCode processor by using the pattern "java& #115;cript" where the numeric character reference s represents the letter 's' in the javascript protocol. This approach allows malicious code to be embedded in a way that bypasses traditional HTML and script filtering mechanisms. The embedded space within the numeric character reference creates a parsing anomaly that enables the javascript payload to execute in the victim's browser context. This technique represents a variant of bypass methods commonly catalogued under CWE-79, which addresses cross-site scripting vulnerabilities in web applications.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal user credentials, redirect victims to malicious websites, or inject malicious content into forum threads. When users view affected posts containing the malicious BBCode, their browsers execute the embedded javascript code, potentially compromising their sessions and personal data. The vulnerability affects all users who view forum posts containing the malicious payload, making it particularly dangerous in community forums where users trust content from other members. This type of vulnerability directly relates to the ATT&CK technique T1566, which describes the use of malicious links and content to compromise user systems through social engineering and script injection.
Security mitigations for this vulnerability require immediate patching of the MyBB software to version 1.1.8 or later, which contains the necessary fixes for proper BBCode sanitization. System administrators should implement comprehensive input validation for all user-generated content, particularly focusing on BBCode processing and URL handling. The fix typically involves stricter sanitization of URL parameters within BBCode tags and the removal of dangerous character sequences that could be used for encoding malicious payloads. Organizations should also consider implementing web application firewalls to detect and block similar encoding patterns and establish monitoring procedures to identify potential exploitation attempts. Additionally, user education about the risks of clicking suspicious links and the importance of keeping forum software updated remains crucial in preventing successful exploitation of such vulnerabilities.