CVE-2014-7939 in Chrome
Summary
by MITRE
Google Chrome before 40.0.2214.91, when the Harmony proxy in Google V8 is enabled, allows remote attackers to bypass the Same Origin Policy via crafted JavaScript code with Proxy.create and console.log calls, related to HTTP responses that lack an "X-Content-Type-Options: nosniff" header.
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Analysis
by VulDB Data Team • 03/06/2022
The vulnerability identified as CVE-2014-7939 represents a critical security flaw in Google Chrome versions prior to 40.0.2214.91 that exploits the Harmony proxy functionality within the V8 JavaScript engine. This vulnerability specifically targets the Same Origin Policy enforcement mechanism that forms a fundamental pillar of web browser security by preventing unauthorized access to resources across different origins. The flaw manifests when the Harmony proxy feature is enabled, creating a pathway for malicious actors to circumvent browser security controls through carefully crafted JavaScript code sequences.
The technical exploitation involves leveraging Proxy.create operations in conjunction with console.log function calls to manipulate HTTP response handling within the browser's JavaScript execution environment. When web servers fail to include the crucial "X-Content-Type-Options: nosniff" header in their HTTP responses, the V8 engine's proxy implementation becomes susceptible to manipulation. This header serves as a security measure that prevents browsers from performing MIME type sniffing and enforces strict content type handling, which is essential for maintaining security boundaries in web applications. The absence of this header creates an exploitable condition where the proxy functionality can be abused to bypass security restrictions.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to perform cross-origin resource access that should normally be restricted. This capability allows malicious actors to potentially access sensitive data from different origins, including cookies, local storage, and other browser-stored information that should remain isolated. The vulnerability's exploitation requires specific conditions including the enabling of Harmony proxy and the presence of vulnerable JavaScript code patterns, but once triggered, it can provide unauthorized access to resources that should be protected by the browser's security model.
This vulnerability aligns with CWE-284, which addresses improper access control mechanisms, and demonstrates how proxy implementations in JavaScript engines can introduce security gaps when not properly integrated with existing browser security policies. The attack vector specifically relates to the ATT&CK technique T1059.007 for JavaScript execution and T1566 for credential access through web-based attacks. The flaw essentially undermines the browser's fundamental security model by allowing attackers to manipulate the proxy layer to bypass the same origin policy enforcement, creating a persistent security risk that affects all users of vulnerable Chrome versions.
Mitigation strategies for CVE-2014-7939 primarily involve updating to Google Chrome version 40.0.2214.91 or later, which includes patches addressing the proxy implementation issue. Additionally, web server administrators should ensure that all HTTP responses include the "X-Content-Type-Options: nosniff" header to prevent MIME type sniffing attacks that could compound the vulnerability. Browser security configurations should disable Harmony proxy functionality when not explicitly required for application compatibility, and organizations should implement comprehensive monitoring to detect suspicious JavaScript execution patterns that might indicate exploitation attempts. Network security controls should also be configured to block potentially malicious JavaScript code that attempts to manipulate proxy objects in ways that could bypass security restrictions.