CVE-2016-1949 in Firefox
Summary
by MITRE
Mozilla Firefox before 44.0.2 does not properly restrict the interaction between Service Workers and plugins, which allows remote attackers to bypass the Same Origin Policy via a crafted web site that triggers spoofed responses to requests that use NPAPI, as demonstrated by a request for a crossdomain.xml file.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-1949 represents a critical security flaw in Mozilla Firefox versions prior to 44.0.2 that fundamentally undermines the browser's security model through improper handling of Service Workers and plugin interactions. This weakness specifically targets the Same Origin Policy implementation, which serves as one of the most fundamental security mechanisms in web browsers. The vulnerability operates by exploiting a design gap where Service Workers can manipulate requests made to plugins, particularly those using the NPAPI (Netscape Plugin Application Programming Interface) architecture, which has been deprecated but still maintained for backward compatibility. The flaw enables malicious actors to craft web pages that can generate spoofed responses to requests that would normally be restricted by security policies, effectively creating a bypass mechanism that allows cross-origin data access.
The technical implementation of this vulnerability leverages the interaction between modern web technologies and legacy plugin systems. Service Workers, which are JavaScript programs that run in the background to manage network requests and cache responses, can intercept and modify requests made to plugins. When a web page triggers a request for a crossdomain.xml file through an NPAPI plugin, the Service Worker can manipulate this interaction to return spoofed responses that appear to originate from the target domain. This creates a scenario where attackers can perform cross-origin resource sharing operations that should be blocked by the browser's security model. The vulnerability specifically affects the way Firefox handles these interactions between the service worker context and plugin execution environments, creating an unexpected pathway for privilege escalation and data exfiltration.
The operational impact of CVE-2016-1949 extends far beyond simple policy bypass, as it represents a sophisticated attack vector that could enable various malicious activities including data theft, cross-site request forgery, and privilege escalation attacks. Attackers could exploit this vulnerability to access sensitive data from different origins that would normally be protected by the Same Origin Policy, potentially compromising user sessions, accessing confidential information, or performing unauthorized actions on behalf of users. The vulnerability is particularly dangerous because it operates at a fundamental level of the browser's security architecture, making it difficult to detect and mitigate. According to CWE-284, this represents an improper access control vulnerability that allows attackers to bypass security restrictions through improper interaction between different security domains. The attack could be executed through a single malicious webpage that triggers the vulnerable interaction, making it highly practical and potentially widespread.
Mitigation strategies for this vulnerability focus primarily on updating to Firefox version 44.0.2 or later, which includes patches that properly restrict the interaction between Service Workers and plugins. Organizations should implement comprehensive browser update policies and ensure all users are running patched versions of Firefox. Additionally, administrators should monitor for any attempts to exploit this vulnerability through network traffic analysis and web application firewalls. The fix implemented by Mozilla addresses the core issue by preventing Service Workers from modifying requests to plugins that could be used to bypass security restrictions. From an ATT&CK framework perspective, this vulnerability maps to T1071.004 (Application Layer Protocol: DNS) and T1566 (Phishing) as attackers could use this flaw to create more convincing phishing attacks by bypassing normal security restrictions. Security teams should also consider implementing browser hardening measures and monitoring for unusual Service Worker activity that might indicate exploitation attempts, particularly around plugin interactions and cross-origin requests that should normally be blocked by security policies.