CVE-2017-3935 in McAfee Network Data Loss Prevention
Summary
by MITRE
Network Data Loss Prevention is vulnerable to MIME type sniffing which allows older versions of Internet Explorer to perform MIME-sniffing on the response body, potentially causing the response body to be interpreted and displayed as a content type other than the intended content type.
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Analysis
by VulDB Data Team • 12/02/2019
The vulnerability described in CVE-2017-3935 represents a critical security flaw in Network Data Loss Prevention systems that stems from improper handling of MIME type detection in web browsers. This issue specifically affects older versions of Internet Explorer which implement aggressive MIME type sniffing behavior, allowing them to override the declared content type of HTTP responses. The vulnerability resides in the server-side response handling where the system fails to properly enforce content type declarations, creating an attack surface that can be exploited by malicious actors to manipulate how web content is rendered in affected browsers.
The technical flaw manifests when Internet Explorer encounters HTTP responses that do not explicitly declare their content type or when the declared type is ambiguous. The browser's MIME-sniffing mechanism attempts to determine the actual content type by analyzing the response body itself, rather than relying on the Content-Type header provided by the server. This behavior, while intended to improve user experience in some scenarios, creates significant security implications when combined with network data loss prevention systems that may not properly sanitize or validate response content. The vulnerability is particularly dangerous because it can cause legitimate content to be interpreted as malicious types, potentially enabling cross-site scripting attacks or other exploitation techniques.
The operational impact of this vulnerability extends beyond simple content rendering issues and can lead to serious security consequences within enterprise environments that rely on network data loss prevention systems. When affected browsers interpret response bodies as different content types, attackers can potentially execute malicious code through techniques such as HTML injection or script execution in contexts where the browser's security policies would normally prevent such actions. This vulnerability particularly affects organizations using older Internet Explorer versions in their enterprise environments, where the browser's aggressive MIME-sniffing behavior can bypass security controls implemented by data loss prevention systems. The risk is compounded when these systems process sensitive data or when users have elevated privileges within the network infrastructure.
Mitigation strategies for CVE-2017-3935 should focus on both server-side configuration and client-side security measures. Organizations should implement proper Content-Type headers with explicit declarations for all HTTP responses, ensuring that the declared content type matches the actual response body content. The use of X-Content-Type-Options: nosniff header is essential as it instructs Internet Explorer and other browsers to strictly adhere to the declared content type rather than attempting MIME-sniffing. Network data loss prevention systems should be configured to enforce strict content validation and sanitization before allowing content to be transmitted to client browsers. Additionally, organizations should consider implementing browser policy controls to disable or restrict MIME-sniffing behavior in older Internet Explorer versions. This vulnerability aligns with CWE-475, which addresses improper handling of undefined values in software, and maps to ATT&CK technique T1059.001 for command and scripting interpreter, as attackers can exploit the MIME-sniffing behavior to execute malicious scripts through content type manipulation. Regular security assessments and browser compatibility testing should be conducted to ensure that all systems properly handle content type declarations and prevent unintended browser behavior that could compromise network security.