CVE-2016-2816 in Firefox
Summary
by MITRE
Mozilla Firefox before 46.0 allows remote attackers to bypass the Content Security Policy (CSP) protection mechanism via the multipart/x-mixed-replace content type.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2816 represents a critical weakness in Mozilla Firefox's Content Security Policy implementation that existed prior to version 46.0. This flaw specifically targets the browser's ability to enforce security restrictions on web content, particularly when processing multipart content types. The issue arises from how Firefox handles the multipart/x-mixed-replace content type which is commonly used for streaming content such as live video feeds or dynamic web page updates. This content type allows servers to send multiple parts of a document sequentially, with each part replacing the previous one in the browser window.
The technical flaw stems from Firefox's insufficient validation of multipart content when it contains embedded scripts or other potentially malicious elements. When a web server sends content using the multipart/x-mixed-replace content type, the browser's CSP enforcement mechanism fails to properly inspect and filter the individual parts of the multipart message. This oversight allows attackers to craft malicious web pages that include script content within multipart responses, effectively bypassing the security protections that CSP is designed to provide. The vulnerability creates a pathway for attackers to circumvent security controls that would normally prevent execution of unauthorized scripts or loading of external resources from untrusted sources.
The operational impact of this vulnerability is significant as it undermines fundamental web security principles that users and organizations rely upon. Attackers can exploit this weakness to inject malicious scripts into web pages, potentially leading to cross-site scripting attacks, data theft, session hijacking, or the execution of arbitrary code within the victim's browser context. The bypass of CSP protection means that even websites with strict security policies can be compromised, as the multipart content type creates an unexpected execution path that the security system does not properly monitor. This vulnerability particularly affects web applications that depend on CSP for protecting against script injection attacks and could enable attackers to escalate privileges or access sensitive information.
The vulnerability aligns with CWE-352, which describes Cross-Site Request Forgery, and relates to the broader category of security misconfigurations that allow bypass of protective mechanisms. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communication and execution through web-based protocols. The mitigation strategy primarily involves updating to Firefox version 46.0 or later where the issue has been resolved through improved content type handling and enhanced CSP enforcement. Organizations should also implement additional monitoring for suspicious multipart content and consider deploying web application firewalls that can detect and block anomalous content type usage patterns. Security teams should review existing CSP policies to ensure they account for multipart content handling and consider implementing additional security layers such as strict transport security enforcement and enhanced browser hardening measures.
This vulnerability demonstrates the complexity of modern web security implementations where seemingly minor content type handling decisions can create significant security gaps. The fix implemented by Mozilla involved strengthening the validation logic for multipart content and ensuring that CSP policies are consistently applied across all content delivery mechanisms, regardless of the content type being processed. The incident underscores the importance of comprehensive security testing that includes edge cases involving various content types and the necessity of maintaining up-to-date security software to protect against known vulnerabilities.