CVE-2016-2817 in Firefox
Summary
by MITRE
The WebExtension sandbox feature in browser/components/extensions/ext-tabs.js in Mozilla Firefox before 46.0 does not properly restrict principal inheritance during chrome.tabs.create and chrome.tabs.update API calls, which allows remote attackers to conduct Universal XSS (UXSS) attacks via a crafted extension that accesses a (1) javascript: or (2) data: URL.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2817 represents a critical security flaw in Mozilla Firefox's WebExtension sandbox implementation that fundamentally undermines the browser's security model. This issue resides within the browser/components/extensions/ext-tabs.js component and affects Firefox versions prior to 46.0, creating a pathway for sophisticated cross-site scripting attacks that bypass traditional security boundaries. The flaw specifically manifests in the improper handling of principal inheritance during chrome.tabs.create and chrome.tabs.update API calls, which are core functions enabling extension developers to manipulate browser tabs programmatically. The vulnerability's severity stems from its ability to allow remote attackers to execute malicious code in the context of any web page, effectively breaking the security isolation that separates browser internals from user content.
The technical mechanism behind this vulnerability involves the WebExtension sandbox's failure to properly enforce security boundaries when processing URL-based operations within tab manipulation APIs. When extensions attempt to create or update tabs using javascript: or data: URLs, the sandbox incorrectly inherits the privileges of the calling context rather than maintaining proper security restrictions. This principal inheritance flaw enables malicious extensions to escalate their privileges and execute arbitrary code with the permissions of the target page, creating a universal cross-site scripting vector that operates across all web content. The vulnerability is particularly dangerous because it leverages legitimate browser APIs to achieve unauthorized access, making detection and prevention significantly more challenging for both users and security systems. According to CWE classification, this represents a weakness in the design of privilege management mechanisms, specifically CWE-284 for improper access control and CWE-79 for cross-site scripting vulnerabilities.
The operational impact of CVE-2016-2817 extends far beyond typical XSS attacks, as it enables attackers to perform Universal XSS attacks that can compromise any web page regardless of its security configuration. Attackers can craft malicious extensions that exploit this vulnerability to inject malicious scripts into web pages, potentially stealing session cookies, credentials, or other sensitive information from users. The attack vector is particularly insidious because it operates through legitimate browser extension mechanisms, making it difficult to distinguish between benign and malicious extensions. This vulnerability creates a persistent threat that can remain undetected for extended periods, as the malicious behavior occurs within the legitimate extension framework rather than through obvious exploit attempts. The attack can be executed through various means including malicious browser extensions downloaded from official stores, making it a significant concern for enterprise security and individual users alike.
Mitigation strategies for CVE-2016-2817 require immediate action to upgrade to Firefox 46.0 or later versions where the vulnerability has been addressed through proper principal inheritance controls. Organizations should implement strict extension management policies, including regular audits of installed extensions and enforcement of extension source restrictions. Security teams should deploy web application firewalls and content security policies that can detect and block suspicious URL patterns, particularly javascript: and data: protocols. The fix implemented by Mozilla involved strengthening the sandbox's principal inheritance mechanisms to prevent privilege escalation during tab manipulation operations, ensuring that extension APIs maintain proper security boundaries. Additionally, users should be educated about the risks of installing extensions from untrusted sources and should regularly review their installed extensions for suspicious activity. This vulnerability highlights the critical importance of maintaining up-to-date browser software and implementing layered security approaches that protect against both known and emerging threats. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the T1068 privilege escalation tactic, where attackers leverage legitimate system tools to gain elevated access rights.