CVE-2018-5108 in Firefox
Summary
by MITRE
A Blob URL can violate origin attribute segregation, allowing it to be accessed from a private browsing tab and for data to be passed between the private browsing tab and a normal tab. This could allow for the leaking of private information specific to the private browsing context. This issue is mitigated by the requirement that the user enter the Blob URL manually in order for the access violation to occur. This vulnerability affects Firefox < 58.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/01/2021
The vulnerability identified as CVE-2018-5108 represents a critical security flaw in Mozilla Firefox browsers prior to version 58, specifically addressing a failure in origin attribute segregation mechanisms that govern how web content interacts across different browsing contexts. This weakness stems from the improper handling of Blob URLs within the browser's security model, creating an avenue for cross-context data leakage that undermines the fundamental isolation principles of private browsing modes. The flaw allows malicious actors to exploit the browser's URL handling system to gain unauthorized access to private browsing tab contents from regular browsing tabs, effectively breaking down the security boundaries that separate sensitive user data from standard browsing sessions. The vulnerability operates through a sophisticated manipulation of the browser's security architecture, where Blob URLs - which are typically restricted to their originating context - can be manually constructed and accessed across different browsing contexts, creating a pathway for information exfiltration.
The technical implementation of this vulnerability exploits the browser's origin-based security model by leveraging the specific mechanism through which Blob URLs are processed and validated. When a user manually enters a Blob URL into the browser's address bar, the system fails to properly enforce the origin attribute restrictions that should prevent cross-context access. This allows a malicious actor to construct a Blob URL that references resources within a private browsing session and subsequently access those resources from a regular browsing tab. The flaw is particularly concerning because it operates under the assumption that user interaction is required for exploitation, yet this requirement does not sufficiently mitigate the security risk given that users may inadvertently navigate to crafted URLs or be tricked into entering them. The vulnerability directly impacts the browser's ability to maintain proper context isolation, which is a core security principle in modern web browsers designed to prevent information leakage between different browsing sessions and user contexts.
The operational impact of CVE-2018-5108 extends beyond simple data leakage to encompass serious privacy violations and potential exploitation of sensitive user information stored in private browsing contexts. This vulnerability could enable attackers to access confidential data such as login credentials, personal communications, financial information, and other sensitive content that users expect to remain isolated within private browsing sessions. The security implications are particularly severe because private browsing modes are explicitly designed to protect user privacy by preventing data persistence and cross-session information leakage. Attackers could potentially use this vulnerability to extract cookies, cached data, form inputs, and other session-specific information that should remain isolated between browsing contexts. The vulnerability creates a persistent threat vector that could be exploited in various attack scenarios including targeted surveillance, credential theft, and privacy invasion, making it a significant concern for users who rely on private browsing for sensitive activities.
Mitigation strategies for this vulnerability primarily focus on immediate browser updates to version 58 or later, where Mozilla implemented specific fixes to address the Blob URL access control mechanisms. Organizations and users should prioritize updating their Firefox installations to ensure protection against this specific exploit, as the vulnerability cannot be effectively mitigated through configuration changes or user behavior modifications alone. The fix implemented by Mozilla addresses the core issue by strengthening the origin attribute validation for Blob URLs and ensuring proper context isolation between private and regular browsing sessions. Security administrators should also implement monitoring systems to detect potential attempts to access Blob URLs in unusual contexts and consider deploying additional security layers such as content security policies that restrict Blob URL usage within sensitive applications. The vulnerability serves as a reminder of the importance of maintaining current browser security patches and highlights the critical need for continuous security assessment of browser components that handle cross-context data access, particularly in environments where privacy-sensitive information is handled regularly.
This vulnerability aligns with CWE-284, which addresses improper access control in software systems, and demonstrates how browser security models can be undermined through insufficient validation of resource access mechanisms. The attack vector corresponds to techniques described in the ATT&CK framework under privilege escalation and credential access categories, specifically targeting the exploitation of browser security boundaries to gain unauthorized access to protected resources. The manual user entry requirement does not adequately address the underlying architectural flaw, indicating a gap in the security model that requires comprehensive review of how browsers handle cross-context resource references and access control enforcement mechanisms.