CVE-2018-12403 in Firefox
Summary
by MITRE
If a site is loaded over a HTTPS connection but loads a favicon resource over HTTP, the mixed content warning is not displayed to users. This vulnerability affects Firefox < 63.
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Analysis
by VulDB Data Team • 06/03/2023
This vulnerability represents a critical mixed content issue in Firefox browser security implementation where the application fails to properly detect and warn users about insecure resource loading within secure contexts. The flaw specifically occurs when a website establishes a secure https connection but subsequently loads favicon resources through unencrypted http protocols, creating a scenario where users remain unaware of potential security risks. This behavior violates fundamental web security principles and demonstrates a failure in Firefox's mixed content blocking mechanisms that should protect users from downgrade attacks and man-in-the-middle scenarios.
The technical root cause of this vulnerability lies in Firefox's inconsistent handling of mixed content warnings, particularly for favicon resources which are typically small icon files used to represent websites in browser tabs and bookmarks. When Firefox encounters a https site that loads favicon content over http, the browser's security subsystem fails to trigger the appropriate mixed content warning, leaving users exposed to potential attacks where malicious actors could intercept or modify the favicon content. This represents a CWE-693 weakness in security mechanism design where the security check fails to properly validate resource integrity in secure contexts, specifically affecting the browser's ability to detect and prevent insecure resource loading.
The operational impact of this vulnerability extends beyond simple user experience concerns to represent a significant security risk in web browsing environments. Users accessing secure websites may unknowingly expose themselves to attacks where favicon resources are modified to include malicious content, redirect users to phishing sites, or serve as attack vectors for more sophisticated exploitation techniques. This vulnerability particularly affects the security posture of organizations relying on Firefox browsers, as it undermines the trust model that secure https connections should provide to users. The issue aligns with ATT&CK technique T1071.004 for application layer protocol manipulation and represents a failure in browser security enforcement that could enable credential theft, data exfiltration, or other malicious activities.
Firefox versions prior to 63 were vulnerable to this issue due to incomplete implementation of mixed content blocking policies that should have applied consistently across all resource types within secure contexts. The vulnerability demonstrates the importance of comprehensive security validation across all browser components, including seemingly innocuous elements like favicons that are often overlooked in security assessments. Organizations should ensure that all browsers are updated to versions that properly implement mixed content warnings for all resource types, particularly given the widespread use of favicon resources and the potential for these resources to be exploited in various attack scenarios. The fix implemented in Firefox 63 likely involved strengthening the mixed content detection logic to ensure that any resource loaded over http within a https context triggers appropriate user warnings and security alerts.