CVE-2016-9903 in Firefox
Summary
by MITRE
Mozilla's add-ons SDK had a world-accessible resource with an HTML injection vulnerability. If an additional vulnerability allowed this resource to be loaded as a document it could allow injecting content and script into an add-on's context. This vulnerability affects Firefox < 50.1.
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Analysis
by VulDB Data Team • 10/08/2022
The vulnerability identified as CVE-2016-9903 resides within Mozilla's Add-ons SDK, specifically targeting the Firefox browser version 50.1 and earlier. This flaw represents a critical security weakness that stems from improper access controls and resource handling within the browser's extension framework. The vulnerability manifests through a world-accessible resource that contains an HTML injection vulnerability, creating a potential attack surface that could be exploited by malicious actors to gain unauthorized access to extension contexts. The flaw specifically affects Firefox versions prior to 50.1, indicating that Mozilla had not yet implemented the necessary protections to address this particular security gap in their browser architecture.
The technical implementation of this vulnerability involves a resource that should not be publicly accessible but remains world-accessible, allowing unauthorized parties to load and manipulate content within the browser's extension environment. When combined with another vulnerability that enables this resource to be loaded as a document, attackers can successfully inject malicious HTML content and scripts directly into the add-on's execution context. This injection capability represents a severe privilege escalation vector that allows attackers to execute arbitrary code within the extension's security boundaries, potentially compromising the entire browser extension ecosystem. The flaw essentially creates a pathway for attackers to bypass normal security restrictions that should prevent external resources from directly influencing extension behavior.
The operational impact of CVE-2016-9903 extends beyond simple code execution, as it fundamentally undermines the security model of Firefox extensions. When successfully exploited, this vulnerability allows attackers to inject content and scripts into an add-on's context, potentially enabling data theft, session hijacking, or complete compromise of user browsing sessions. The attack surface is particularly concerning because it targets the core extension framework that many users depend on for enhanced browser functionality, making the exploitation impact widespread across the Firefox user base. This vulnerability could be leveraged to create persistent backdoors within browser extensions, enabling long-term surveillance or manipulation of user activities without detection.
Security professionals should note that this vulnerability aligns with CWE-20, which describes improper input validation, and CWE-79, which covers HTML injection flaws. The attack pattern follows the methodology outlined in the ATT&CK framework under T1190 for exploitation of remote services and T1059 for execution through scripting. Organizations and users must prioritize immediate remediation by updating to Firefox version 50.1 or later, which includes the necessary patches to address the world-accessible resource issue. Additionally, administrators should implement network monitoring to detect potential exploitation attempts and consider temporary disabling of vulnerable extensions until full patch deployment is achieved. The vulnerability demonstrates the critical importance of proper resource access controls and the potential consequences when such controls fail within complex browser extension architectures.