Can you explain this vulnerability to me?

This vulnerability is a stored Cross-Site Scripting (XSS) issue in the Citizen skin of MediaWiki. It occurs because various date messages returned by the function Language::userDate are inserted into raw HTML without proper escaping. This allows any user who can edit these date messages (typically those with the 'editinterface' permission but not 'editsitejs') to inject arbitrary HTML or JavaScript into the web page's DOM. The injected malicious code can then execute in the browsers of users viewing the affected pages, potentially leading to unauthorized actions or data exposure. The vulnerability is fixed by properly escaping user inputs and outputs, using safe DOM manipulation methods, and improving message parsing to prevent injection of malicious content. [1, 2]

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How can this vulnerability impact me? :

If exploited, this vulnerability can allow attackers to inject malicious scripts into the MediaWiki pages using the Citizen skin. This can lead to unauthorized access to sensitive information (confidentiality impact), unauthorized modification of data (integrity impact), and potentially other malicious actions executed in the context of the affected wiki. The exploit requires the attacker to have high privileges (logged-in user with 'editinterface' rights) but no user interaction is needed once the malicious content is injected. This can compromise the security and trustworthiness of the wiki environment. [2]

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How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability can be detected by checking if the MediaWiki Citizen skin is in use and if the system allows users with the 'editinterface' permission to edit date messages that are rendered without proper escaping. Specifically, you can inspect the HTML output of pages using the Citizen skin for unescaped HTML in date messages, especially within <time> elements. To detect potential exploitation, monitor HTTP requests with the 'uselang' parameter set to unusual or malicious values (e.g., 'x-xss') while logged in. Commands to assist detection include using curl or wget to fetch pages with crafted 'uselang' parameters and inspecting the response for injected HTML or scripts. For example: curl -i 'https://yourwiki.example.com/wiki/Page?uselang=x-xss' --cookie 'your_login_cookie' Additionally, review user permissions to identify if any groups have 'editinterface' but not 'editsitejs', which increases risk. Since the vulnerability involves stored XSS via interface message edits, auditing recent edits to interface messages for suspicious content is also recommended. [2]

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What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation steps include: 1. Upgrade the MediaWiki Citizen skin to version 3.3.1 or later, where the vulnerability is fixed. 2. Restrict or review user permissions to ensure that only trusted users have the 'editinterface' right, especially if they do not have 'editsitejs'. 3. Audit and sanitize any interface messages or date messages that could have been edited to include malicious HTML. 4. Apply the patch from commit 93c36ac778397e0e7c46cf7adb1e5d848265f1bd which enforces proper escaping and safe DOM manipulation to prevent stored XSS. 5. Monitor for suspicious activity involving the 'uselang' parameter or unusual HTML content in user date messages. These steps help prevent exploitation by closing the injection vectors and limiting the ability of attackers to insert malicious scripts. [1, 2]

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