CVE-2018-5164 in Firefox
Summary
by MITRE
Content Security Policy (CSP) is not applied correctly to all parts of multipart content sent with the "multipart/x-mixed-replace" MIME type. This could allow for script to run where CSP should block it, allowing for cross-site scripting (XSS) and other attacks. This vulnerability affects Firefox < 60.
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Analysis
by VulDB Data Team • 03/11/2023
The vulnerability described in CVE-2018-5164 represents a critical security flaw in Firefox's implementation of Content Security Policy enforcement mechanisms. This issue specifically impacts how the browser handles multipart content streams using the "multipart/x-mixed-replace" MIME type, which is commonly used for server-sent events and live video feeds. The flaw occurs because Firefox fails to properly apply CSP directives to all components of multipart content, creating a bypass mechanism that allows malicious scripts to execute despite CSP restrictions designed to prevent such attacks. This vulnerability directly undermines the fundamental security principle of CSP, which is intended to prevent unauthorized script execution by defining which sources of content are permitted to be loaded and executed within a web page context.
The technical implementation of this vulnerability stems from Firefox's inadequate handling of CSP enforcement during the processing of multipart content streams. When a web page receives content through the "multipart/x-mixed-replace" MIME type, the browser should enforce CSP policies consistently across all parts of the multipart response. However, the flaw allows certain portions of the multipart content to bypass CSP restrictions, particularly affecting script execution within the multipart stream. This misconfiguration creates a scenario where an attacker can inject malicious scripts into parts of the multipart content that should be blocked by CSP, effectively neutralizing the security protections that users expect. The vulnerability specifically affects Firefox versions prior to 60, indicating this was a targeted issue within a particular browser release cycle.
The operational impact of CVE-2018-5164 is significant for web application security and user protection. This vulnerability enables attackers to perform cross-site scripting attacks by exploiting the CSP bypass mechanism, potentially allowing for session hijacking, data theft, and other malicious activities. When an attacker controls a server that sends content using the "multipart/x-mixed-replace" MIME type, they can inject scripts that execute in the context of the victim's browser session. The vulnerability is particularly dangerous because it operates silently in the background, making it difficult for users to detect that their security protections have been bypassed. This type of attack can be particularly effective in environments where users trust the content source but are unaware that malicious scripts can execute due to the CSP enforcement gap.
From a cybersecurity perspective, this vulnerability aligns with CWE-1021, which addresses "Improper Restriction of Rendered UI Elements," and relates to the broader category of CSP bypass techniques documented in various ATT&CK frameworks under the T1211 category for "Exploitation for Defense Evasion." The flaw demonstrates how browser-specific implementation gaps can create security vulnerabilities that attackers can leverage to circumvent web application security controls. Organizations relying on Firefox for web browsing and application development must understand that this vulnerability affects their security posture when users access web content through vulnerable browser versions. The impact extends beyond simple XSS attacks to potentially enable more sophisticated attacks such as credential theft, privilege escalation, and persistent malicious code execution within user sessions.
The recommended mitigation for CVE-2018-5164 involves immediate upgrading of Firefox to version 60 or later, where the CSP enforcement for multipart content has been properly implemented. System administrators should also implement additional security measures such as monitoring for unusual multipart content patterns and ensuring that CSP policies are comprehensive and include appropriate directives for all content types. Web application developers should consider implementing additional client-side security controls and regularly audit their applications for potential CSP bypass vulnerabilities. Organizations should also maintain updated threat intelligence feeds to identify and respond to similar browser-specific vulnerabilities that may affect their security infrastructure. The vulnerability serves as a reminder of the critical importance of keeping browser software updated and maintaining comprehensive security testing procedures that include browser-specific vulnerability assessments.