CVE-2017-5408 in Firefox
Summary
by MITRE
Video files loaded video captions cross-origin without checking for the presence of CORS headers permitting such cross-origin use, leading to potential information disclosure for video captions. This vulnerability affects Firefox < 52, Firefox ESR < 45.8, Thunderbird < 52, and Thunderbird < 45.8.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability described in CVE-2017-5408 represents a critical security flaw in Mozilla Firefox and Thunderbird browsers related to cross-origin resource sharing implementation for video caption files. This issue stems from the browser's failure to properly validate cross-origin access controls when processing video content with embedded captions, creating a potential avenue for unauthorized information disclosure. The flaw specifically impacts versions of Firefox prior to 52 and Firefox ESR prior to 45.8, as well as corresponding versions of Thunderbird browser applications.
The technical root cause of this vulnerability lies in the improper handling of cross-origin requests for video caption files within the browser's media processing pipeline. When a web page loads a video file that contains embedded captions, the browser should verify that appropriate CORS headers are present to permit cross-origin access to these caption resources. However, the vulnerable implementations failed to perform this crucial validation step, allowing malicious actors to potentially access caption data from different origins without proper authorization. This behavior violates fundamental web security principles that govern resource sharing across domain boundaries.
The operational impact of this vulnerability extends beyond simple information disclosure, as video captions often contain sensitive metadata, contextual information, or proprietary content that could be exploited by attackers. When cross-origin caption files are loaded without proper CORS validation, threat actors could potentially extract private information embedded within caption streams, including personal identifiers, location data, or other confidential content that might be included in caption files for accessibility or localization purposes. This risk is particularly concerning in environments where multimedia content contains classified or sensitive information that should remain protected from unauthorized access.
From a security framework perspective, this vulnerability aligns with CWE-346, which addresses "Origin Validation Error" in web applications, and represents a clear violation of the CORS security model as defined by web standards. The flaw also maps to ATT&CK technique T1071.004, which covers "Application Layer Protocol: DNS" in the context of information gathering through web protocol manipulation. Organizations using affected browser versions face significant risk of data leakage, particularly in scenarios where video content is served from multiple domains or when captions contain sensitive information that should remain isolated from unauthorized access.
Mitigation strategies for this vulnerability require immediate patching of affected browser installations to the latest supported versions that properly implement CORS validation for video caption resources. System administrators should prioritize updating Firefox and Thunderbird installations across all endpoints, particularly in enterprise environments where multimedia content processing occurs. Additionally, network administrators can implement content filtering rules to restrict cross-origin video content access, though this represents a secondary mitigation approach. The vulnerability highlights the importance of proper CORS implementation in multimedia applications and underscores the necessity of thorough security testing for all browser components that handle cross-origin resource requests. Organizations should also consider implementing network monitoring to detect anomalous cross-origin requests for video caption files, as part of their broader security operations center procedures for identifying potential exploitation attempts.