CVE-2015-7191 in Firefox
Summary
by MITRE
Mozilla Firefox before 42.0 on Android improperly restricts URL strings in intents, which allows attackers to conduct cross-site scripting (XSS) attacks via vectors involving an intent: URL and fallback navigation, aka "Universal XSS (UXSS)."
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Analysis
by VulDB Data Team • 06/26/2022
The vulnerability identified as CVE-2015-7191 represents a critical security flaw in Mozilla Firefox versions prior to 42.0 on Android platforms. This issue stems from improper handling of URL strings within intent mechanisms, creating a pathway for sophisticated cross-site scripting attacks that can bypass traditional security boundaries. The vulnerability specifically affects the Android version of Firefox, where the browser's intent processing system fails to adequately sanitize URL parameters, allowing malicious actors to craft specially crafted URLs that can execute arbitrary code within the browser context.
The technical implementation of this vulnerability involves Firefox's Android-specific intent handling system, which is designed to allow applications to request actions from other applications through well-formed URLs. When Firefox encounters an intent: URL, it processes the URL parameters to determine the appropriate action to take. However, the vulnerability occurs because Firefox fails to properly validate and sanitize the URL components before executing the intent, creating a condition where attacker-controlled input can influence the execution flow. This flaw enables what security researchers classify as a universal cross-site scripting vulnerability, where the attack can potentially target any web application regardless of its security measures.
The operational impact of CVE-2015-7191 extends beyond typical XSS scenarios due to its universal nature and the privileged context in which it operates. Attackers can exploit this vulnerability by crafting malicious intent: URLs that, when clicked by a victim using an affected Firefox version, can execute malicious scripts within the browser's context. This capability allows for complete compromise of the user's browsing session, enabling attacks such as cookie theft, session hijacking, and arbitrary code execution. The vulnerability particularly affects Android users who may be tricked into clicking malicious links through phishing campaigns or compromised websites, as the attack can occur without requiring user interaction beyond simply visiting the malicious page.
From a security framework perspective, this vulnerability aligns with CWE-79, which describes Cross-Site Scripting vulnerabilities, and represents a sophisticated variant that leverages Android's intent system. The ATT&CK framework categorizes this as a technique involving code injection through web browsers, specifically targeting the application layer where user input is processed. The vulnerability's classification as universal XSS (UXSS) indicates that it operates outside the typical boundaries of browser security models, potentially allowing attackers to bypass same-origin policies and execute code with the privileges of the user's browsing session.
Mitigation strategies for CVE-2015-7191 require immediate patching of affected Firefox versions to 42.0 or later, where Mozilla implemented proper URL sanitization and intent validation mechanisms. Organizations should also deploy network-based protections such as web application firewalls that can detect and block malicious intent: URLs, while security teams should monitor for indicators of compromise related to this specific vulnerability. Additionally, user education regarding the dangers of clicking unknown links and the importance of keeping browser software updated remains crucial. The vulnerability underscores the importance of proper input validation in mobile browser implementations and highlights how platform-specific features like Android intents can introduce unexpected security attack surfaces when not properly secured.