Internet Explorer Protected Mode

Internet Explorer Protected Mode
Name	Internet Explorer Protected Mode
Developer	Microsoft
Released	2009
Operating system	Windows Vista, Windows 7, Windows Server 2008
Genre	Web browser security
License	Proprietary

Internet Explorer Protected Mode is a sandboxing feature introduced by Microsoft for Internet Explorer 7 and Internet Explorer 8 on Windows Vista and later applied in Internet Explorer 9 and Internet Explorer 10. It aimed to reduce the impact of remote code execution and privilege escalation by isolating browser processes within a constrained environment tied to User Account Control. The feature interacts with Windows kernel components, Internet Explorer security zones, and enterprise management tools to control rights and file system access.

Overview

Protected Mode was introduced as part of Microsoft’s response to rising threats chronicled around incidents involving Conficker, Stuxnet, and high-profile exploits disclosed at conferences like Black Hat and CanSecWest. It leverages the Integrity levels model in Windows Vista and later to run the brokered Internet Explorer process at a Low Integrity level, reducing the impact of exploitation similar in aim to techniques used in Google Chrome’s multi-process sandbox and the OpenBSD pledge/privsep approach. Administrators encountered Protected Mode during deployments of Windows Server 2008 and Windows 7 in enterprise settings alongside legacy compatibility features such as Compatibility View.

Design and Architecture

Protected Mode’s architecture is centered on creating a Low Integrity process separated from higher-privilege components such as the Desktop Window Manager and Windows Shell. It relies on the Mandatory Integrity Control mechanism introduced in Windows Vista to assign Low, Medium, High, and System integrity levels to processes and objects. The model uses an AppContainer-like isolation for later versions, while earlier implementations used Low Integrity token restrictions mediated by the Local Security Authority and Windows API calls like CreateRestrictedToken. Communication between the low-privilege renderer and elevated broker components occurred via constrained inter-process communication channels similar to RPC patterns used in Microsoft COM and the Component Object Model.

Protected Mode enforced restrictions on the Windows Registry, file system under %USERPROFILE%, and access to Internet Explorer extensions through a policy gatekeeping mechanism comparable to controls in Windows Group Policy and configuration management tools such as System Center Configuration Manager. The architecture accounted for mixing of protected and unprotected frames by segregating zones—Internet, Local Intranet, Trusted Sites, and Restricted Sites—as defined in the Zone.Identifier model.

Security Features and Mechanisms

Key mechanisms included running the Internet Explorer tab process at Low Integrity, dropping privileges using restricted tokens, and preventing writes outside per-user temporary locations and areas explicitly allowed by Access Control Lists. The implementation constrained ActiveX controls and browser helper objects, integrating with ActiveX killbits and marking certain extensions as requiring elevation handled by the broker process. It used file and registry virtualization patterns and leveraged Address Space Layout Randomization and Data Execution Prevention provided by the Windows kernel to mitigate exploitation techniques observed in vulnerabilities reported to Microsoft through Zero Day Initiative and Microsoft Security Response Center workflows.

Protected Mode also integrated with Attachment Execution Services and the URLMon protocol handling to control download execution paths, and signaled elevation requirements to User Account Control prompts when a privileged action was necessary, in a manner consistent with Microsoft Trustworthy Computing initiatives.

Compatibility and Limitations

Protected Mode introduced trade-offs impacting compatibility with legacy add-ons, intranet applications, and enterprise management suites such as Active Directory scripts and legacy COM objects. Many third-party toolchains and enterprise web applications that assumed medium or high process integrity required reengineering or the use of Trusted Sites exceptions in Group Policy. The feature did not fully mitigate kernel-level exploits or flaws in third-party drivers implicated in attacks like those distributed by exploit kits demonstrated at DEF CON. Some hardware-accelerated features tied to DirectX and the Windows Presentation Foundation required brokered access, complicating rendering performance and integration with multimedia components.

Configuration and Management

System administrators controlled Protected Mode through mechanisms in Group Policy Editor, Internet Options, and registry-based policy keys managed via Active Directory Group Policy. IT departments often used Trusted Sites and Local Intranet zone assignments to exempt internal resources, and leveraged management tools such as System Center and orchestration via Windows PowerShell to deploy consistent configurations. Auditing of Protected Mode behavior relied on Windows Event Log channels and tools used in enterprise security operations centers like Splunk or Microsoft Operations Manager for incident response workflows.

Vulnerabilities and Criticisms

Despite reducing many attack vectors, Protected Mode faced criticism for incomplete coverage against sophisticated chain exploits that combined renderer bugs with kernel or driver vulnerabilities; incidents disclosed at CanSecWest and public advisories from CERT Coordination Center highlighted chained exploit techniques. Researchers from institutions such as Google Project Zero and independent teams published bypasses that exploited trust relationships, COM elevation paths, and signed driver weaknesses. Critics also pointed to usability impacts, increased support burden for IT departments managing legacy intranet applications, and the potential for configuration errors in Group Policy to inadvertently disable protections.

Legacy and Deprecation

As Microsoft shifted focus to Microsoft Edge and the Chromium-based browser model, Protected Mode remained a legacy mitigation tied to the lifecycle of Internet Explorer, de-emphasized in modern Windows editions and eventually deprecated alongside Internet Explorer itself. Concepts pioneered by Protected Mode influenced sandboxing models in Microsoft Edge and cross-vendor efforts in browser hardening seen in Chromium and Firefox project designs. The feature remains a study point in security retrospectives dealing with browser isolation, sandbox evasion research, and enterprise migration efforts away from legacy Internet Explorer dependencies.

Category:Internet Explorer Category:Microsoft security technologies