CVE-2018-5116 in Firefox
Summary
by MITRE
WebExtensions with the "ActiveTab" permission are able to access frames hosted within the active tab even if the frames are cross-origin. Malicious extensions can inject frames from arbitrary origins into the loaded page and then interact with them, bypassing same-origin user expectations with this permission. This vulnerability affects Firefox < 58.
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Analysis
by VulDB Data Team • 07/20/2024
The vulnerability described in CVE-2018-5116 represents a critical security flaw in Firefox's WebExtensions implementation that fundamentally undermines the same-origin policy enforcement mechanisms. This issue specifically targets extensions that request the "ActiveTab" permission, which is designed to allow extensions to interact with the currently active browser tab while maintaining appropriate security boundaries. The flaw enables malicious extensions to bypass cross-origin restrictions that should normally prevent access to content from different origins, creating a significant attack surface that could be exploited by threat actors.
The technical implementation of this vulnerability stems from how Firefox processes the ActiveTab permission within its WebExtensions framework. When an extension requests this permission, it should theoretically only be able to access the active tab's content while respecting cross-origin boundaries. However, the flaw allows extensions to inject arbitrary frames from different origins into the active tab and then interact with these frames as if they were part of the same origin. This bypass occurs at the frame-level access control mechanism, where the browser fails to properly enforce same-origin policies when dealing with dynamically injected content within the active tab context.
The operational impact of this vulnerability is substantial as it enables sophisticated attacks that can harvest sensitive information from cross-origin frames, manipulate user interactions, and potentially execute malicious code within the context of the active tab. Attackers could craft malicious extensions that inject phishing frames or frames containing exploit code, then access and manipulate these frames to steal session tokens, credentials, or other sensitive data. The vulnerability effectively undermines user expectations about browser security boundaries and could be leveraged to perform advanced persistent threats against users who have installed malicious extensions.
Security researchers have classified this vulnerability under CWE-284, which deals with improper access control mechanisms, and it aligns with ATT&CK techniques related to privilege escalation and credential access. The flaw demonstrates how browser extension permissions can be abused to circumvent fundamental web security models, particularly the same-origin policy that forms the cornerstone of web application security. Organizations and users should be particularly concerned as this vulnerability affects Firefox versions prior to 58, representing a significant window of exposure for users who had not yet updated their browsers. The remediation requires updating to Firefox version 58 or later, where the WebExtensions framework properly enforces cross-origin restrictions even when the ActiveTab permission is granted.
This vulnerability highlights the complexity of implementing secure extension frameworks in modern browsers and underscores the importance of rigorous security testing for browser permission models. The issue demonstrates how seemingly benign permission requests can be exploited to create security holes that affect the entire browser ecosystem, emphasizing the need for continuous security auditing of browser features and extension APIs. The fix implemented by Mozilla involved strengthening the frame access controls within the WebExtensions system to properly enforce same-origin policies regardless of the permissions granted to extensions, thereby restoring the expected security boundaries for users.