CVE-2012-4203 in Firefox
Summary
by MITRE
The New Tab page in Mozilla Firefox before 17.0 uses a privileged context for execution of JavaScript code by bookmarklets, which allows user-assisted remote attackers to run arbitrary programs by leveraging a javascript: URL in a bookmark.
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Analysis
by VulDB Data Team • 01/31/2018
The vulnerability described in CVE-2012-4203 represents a critical privilege escalation issue within Mozilla Firefox's New Tab page functionality. This flaw existed in Firefox versions prior to 17.0 and specifically targeted the security model governing how JavaScript code executes within the browser's privileged context. The vulnerability stems from the improper handling of bookmarklets on the New Tab page, where malicious actors could exploit this weakness to execute arbitrary code with elevated privileges.
The technical implementation of this vulnerability involves the use of javascript: URLs within bookmarks to manipulate the execution environment of the New Tab page. When a user visits the New Tab page, Firefox would execute bookmarklets in a privileged context that should normally be restricted to prevent unauthorized code execution. However, the flaw allowed attackers to craft malicious bookmarklets that would execute with the same privileges as the browser itself, effectively bypassing the normal security boundaries that separate user content from privileged browser operations. This privilege escalation occurred because the bookmarklet execution environment did not properly validate or sanitize the JavaScript code being executed, creating an attack vector that could be leveraged by remote adversaries.
The operational impact of this vulnerability is severe as it provides attackers with the ability to execute arbitrary programs on affected systems without requiring any local privileges or user interaction beyond visiting a malicious website. The user-assisted nature of the attack means that an attacker needs to convince a user to click on a malicious bookmark or visit a compromised website containing malicious JavaScript code. Once executed, the malicious code could perform actions such as installing malware, modifying system files, accessing sensitive data, or even taking complete control of the affected system. This vulnerability directly violates the principle of least privilege and could be exploited in conjunction with other attacks to create a complete compromise of the user's browsing environment.
The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access control issues in software systems. It also maps to ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" and T1547.001 for "Registry Run Keys / Startup Folder" as attackers could leverage this vulnerability to establish persistence mechanisms. Organizations should immediately update to Firefox version 17.0 or later where this vulnerability has been patched. The fix implemented by Mozilla involved modifying the security model of the New Tab page to ensure that bookmarklets execute in a restricted context that does not provide elevated privileges. Additionally, administrators should implement browser security policies, disable unnecessary bookmark functionality, and educate users about the risks of clicking on untrusted links or bookmarklets. Regular security audits of browser configurations and monitoring for suspicious bookmark activity can help detect potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date software and understanding the privilege models implemented in modern browsers to prevent unauthorized code execution in privileged contexts.