CVE-2018-5776 in WordPress
Summary
by MITRE
WordPress before 4.9.2 has XSS in the Flash fallback files in MediaElement (under wp-includes/js/mediaelement).
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Analysis
by VulDB Data Team • 02/02/2023
WordPress versions prior to 4.9.2 contained a cross-site scripting vulnerability in the MediaElement flash fallback files located within the wp-includes/js/mediaelement directory. This vulnerability affected the media player component that WordPress uses to handle audio and video content, specifically when the system falls back to flash-based playback for browsers that do not support HTML5 media elements. The flaw originated from insufficient input validation and output encoding within the MediaElement library that WordPress incorporates, allowing malicious actors to inject malicious scripts through crafted media file metadata or player configuration parameters. The vulnerability was particularly concerning because it could be exploited by attackers who had the ability to upload or modify media files, potentially leading to unauthorized access or data theft from users who viewed compromised media content.
The technical implementation of this vulnerability involved the improper handling of user-supplied data within the flash fallback mechanism of the media player. When WordPress encountered media files that required flash fallback, the system would process and embed user-provided parameters without adequate sanitization, creating an opening for XSS attacks. The attack surface was expanded by the fact that the MediaElement library was integrated directly into WordPress core, making it accessible to all WordPress installations running vulnerable versions. This particular vulnerability aligned with CWE-79, which describes cross-site scripting flaws due to improper output encoding, and could be leveraged by threat actors to execute malicious scripts in the context of a user's browser session.
The operational impact of this vulnerability was significant for WordPress users and administrators, as it provided attackers with a potential vector for session hijacking, credential theft, or redirection to malicious sites. Users with administrative privileges were at greater risk since they could be targeted through compromised media uploads that would execute malicious scripts when viewed by other users. The vulnerability was particularly dangerous in multi-user environments where media uploads were common, such as news sites, blogs, or collaborative platforms. Attackers could exploit this weakness by uploading media files with malicious metadata or by manipulating existing media player configurations to inject harmful JavaScript code that would execute when users interacted with the media content.
Organizations and WordPress administrators should have immediately updated to WordPress version 4.9.2 or later to remediate this vulnerability, as it was a critical security issue affecting the core media handling functionality. The recommended mitigation strategy included not only updating WordPress but also implementing proper input validation for all media uploads and monitoring for suspicious file modifications. Security teams should have deployed web application firewalls to detect and block potential XSS payloads, while also conducting thorough audits of existing media content to identify any previously compromised files. Additionally, administrators were advised to review user permissions and implement content security policies to limit the potential damage from successful exploitation attempts, following ATT&CK framework techniques related to credential access and execution through web applications. The vulnerability highlighted the importance of keeping third-party libraries updated and implementing robust security measures for media handling components within content management systems.