CVE-2017-0366 in MediaWiki
Summary
by MITRE
Mediawiki before 1.28.1 / 1.27.2 / 1.23.16 contains a flaw allowing to evade SVG filter using default attribute values in DTD declaration.
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Analysis
by VulDB Data Team • 02/27/2023
The vulnerability identified as CVE-2017-0366 represents a critical security flaw in MediaWiki versions prior to 1.28.1, 1.27.2, and 1.23.16 that stems from improper handling of SVG filter attributes within XML DTD declarations. This issue allows attackers to bypass security restrictions by leveraging default attribute values defined in Document Type Definition files. The vulnerability specifically affects the sanitization mechanisms that MediaWiki employs when processing SVG content, which is commonly used for embedding graphics and diagrams within wiki pages. When MediaWiki processes SVG files, it must validate and sanitize the content to prevent malicious code execution, but the flaw in the DTD attribute handling permits attackers to inject potentially harmful elements that would otherwise be blocked by the security filters.
The technical root cause of this vulnerability lies in how MediaWiki's SVG sanitization logic interprets default attribute values specified in DTD declarations. When an SVG file contains a DTD with default attribute values, the parser may not properly validate these defaults against the expected security parameters, allowing malicious SVG content to slip through the validation process. This occurs because the sanitization routines do not adequately account for the behavior of default attribute values in XML DTDs, which can be used to specify fallback values for attributes that are not explicitly defined in the SVG content. The flaw essentially creates a bypass mechanism where attackers can exploit the default value resolution process to inject content that appears legitimate but contains hidden malicious elements.
The operational impact of this vulnerability extends beyond simple content injection, as it can potentially enable attackers to execute arbitrary code or perform cross-site scripting attacks when users view affected SVG content within MediaWiki environments. Since MediaWiki is widely used for collaborative platforms, wikis, and documentation systems, the exploitation of this vulnerability could affect numerous websites and organizations that rely on the platform. The vulnerability is particularly concerning because SVG files are commonly used for diagrams, charts, and other visual elements in wiki content, making it a frequent vector for exploitation. When users view pages containing maliciously crafted SVG files, the default attribute values in DTD declarations can be leveraged to execute unintended operations, potentially leading to data theft, session hijacking, or further compromise of the affected systems.
This vulnerability aligns with CWE-20, which addresses "Improper Input Validation," and specifically relates to improper handling of XML DTD declarations and their default attribute values. The flaw demonstrates characteristics consistent with ATT&CK technique T1203, "Exploitation for Client Execution," as it enables attackers to execute malicious code through compromised SVG content. Organizations using MediaWiki should prioritize immediate patching to address this vulnerability, as the default attribute value bypass mechanism can be exploited without user interaction once malicious SVG content is uploaded to the platform. The recommended mitigation strategy involves upgrading to MediaWiki version 1.28.1 or higher, which includes enhanced SVG sanitization routines that properly handle DTD declarations and their default attribute values. Additionally, administrators should implement strict file upload policies and content validation measures to further reduce the risk of exploitation, particularly for user-generated content that may include SVG files.