CVE-2016-6333 in MediaWiki
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the CSS user subpage preview feature in MediaWiki before 1.23.15, 1.26.x before 1.26.4, and 1.27.x before 1.27.1 allows remote attackers to inject arbitrary web script or HTML via the edit box in Special:MyPage/common.css.
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Analysis
by VulDB Data Team • 04/21/2017
The vulnerability identified as CVE-2016-6333 represents a critical cross-site scripting flaw within MediaWiki's CSS user subpage preview functionality. This security weakness exists in multiple versions of the popular wiki platform, specifically affecting releases prior to 1.23.15, 1.26.4, and 1.27.1. The flaw manifests in the Special:MyPage/common.css page where users can preview their CSS modifications before saving them. Attackers can exploit this vulnerability by injecting malicious scripts or HTML code directly into the edit box of the CSS preview feature, which then gets executed in the context of other users' browsers when they view the affected page.
The technical mechanism behind this vulnerability stems from inadequate input sanitization within the CSS preview subsystem. When users enter content into the edit box for their CSS modifications, the system fails to properly escape or validate the input before rendering it in the preview window. This allows malicious actors to inject script tags, javascript code, or other HTML elements that execute in the browser context of legitimate users. The vulnerability specifically affects the preview functionality rather than the actual saving mechanism, making it particularly insidious as users may not realize they are being exposed to malicious code during what should be a safe preview operation. This issue falls under CWE-79 which categorizes cross-site scripting vulnerabilities as a result of insufficient input validation and output encoding.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to perform various malicious activities through the compromised user sessions. An attacker could inject scripts that steal session cookies, redirect users to phishing sites, or perform actions on behalf of authenticated users. Given that MediaWiki is widely used in enterprise environments, educational institutions, and collaborative platforms, this vulnerability could potentially compromise entire user bases. The preview feature is commonly used by administrators and power users who may have elevated privileges, making the attack surface even more significant. This vulnerability aligns with ATT&CK technique T1566 which covers credential access through phishing and social engineering methods, as users might be tricked into viewing malicious content within the wiki interface.
Organizations using affected MediaWiki versions should implement immediate mitigations including upgrading to patched versions, implementing proper input validation, and deploying content security policies to limit script execution. Administrators should also consider disabling the preview feature temporarily while applying security patches, and monitoring user activity for signs of exploitation attempts. The vulnerability highlights the importance of sanitizing all user inputs in web applications, particularly in features that render user-generated content. Additionally, organizations should conduct security audits of their wiki configurations to ensure proper access controls and input validation mechanisms are in place to prevent similar vulnerabilities from arising in other components of their web infrastructure.