CVE-2011-1579 in MediaWiki
Summary
by MITRE
The checkCss function in includes/Sanitizer.php in the wikitext parser in MediaWiki before 1.16.3 does not properly validate Cascading Style Sheets (CSS) token sequences, which allows remote attackers to conduct cross-site scripting (XSS) attacks or obtain sensitive information by using the \2f\2a and \2a\2f hex strings to surround CSS comments.
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Analysis
by VulDB Data Team • 11/05/2021
The vulnerability identified as CVE-2011-1579 represents a critical security flaw in the MediaWiki wikitext parser that existed prior to version 1.16.3. This issue resides within the checkCss function located in the includes/Sanitizer.php file, which is responsible for sanitizing and validating CSS content within wiki pages. The flaw stems from inadequate validation of CSS token sequences, creating a pathway for malicious actors to exploit the system through carefully crafted CSS code that bypasses normal security measures.
The technical mechanism behind this vulnerability involves the improper handling of CSS comment syntax through specific hex string sequences. Attackers can utilize the hex values \2f\2a and \2a\2f to construct CSS comments that circumvent the validation logic implemented in the checkCss function. These sequences translate to forward slash and asterisk characters respectively, allowing malicious code to be embedded within CSS comments that are not properly sanitized. When the MediaWiki parser encounters these specially crafted CSS sequences, it fails to recognize them as potentially malicious content, thereby permitting the execution of cross-site scripting payloads or the extraction of sensitive information from the affected system.
The operational impact of this vulnerability extends beyond simple XSS attacks to encompass potential information disclosure scenarios that could compromise user data and system integrity. Remote attackers leveraging this flaw can inject malicious CSS code that executes within the context of other users' browsers, potentially stealing session cookies, redirecting users to malicious sites, or extracting sensitive information from wiki pages. Additionally, the vulnerability may enable attackers to bypass security measures that rely on CSS validation, creating a broader attack surface that could compromise the overall security posture of MediaWiki installations. The vulnerability's persistence across multiple versions of the software indicates a fundamental flaw in the CSS sanitization logic that required significant code reengineering to resolve properly.
The security implications of this vulnerability align with CWE-79, which addresses cross-site scripting flaws in web applications, and specifically relates to the improper neutralization of special elements in CSS contexts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control through web application exploitation, specifically T1071.004 for application layer protocols and T1566 for credential access through malicious web content. The vulnerability demonstrates how seemingly benign parsing functions can create significant security risks when input validation is insufficient, particularly in environments where users can submit content that gets rendered in web browsers. Organizations running MediaWiki systems were advised to upgrade to version 1.16.3 or later to address this vulnerability, as the fix involved comprehensive reworking of the CSS sanitization logic to properly handle all CSS comment syntax variations and prevent the exploitation of hex string sequences that could be used to bypass security checks.