CVE-2011-1894 in Windows
Summary
by MITRE
The MHTML protocol handler in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly handle a MIME format in a request for embedded content in an HTML document, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted EMBED element in a web page that is visited in Internet Explorer, aka "MHTML Mime-Formatted Request Vulnerability."
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Analysis
by VulDB Data Team • 01/13/2025
The CVE-2011-1894 vulnerability represents a critical cross-site scripting flaw in Microsoft's handling of MHTML protocol requests within Internet Explorer across multiple Windows operating systems. This vulnerability specifically affects Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, as well as Windows 7 Gold and SP1. The issue stems from the improper processing of MIME format requests within HTML documents, particularly when handling embedded content through EMBED elements. The vulnerability operates at the protocol handler level where MHTML content is processed, creating a pathway for malicious actors to inject arbitrary script code that executes in the context of the victim's browser session. This flaw falls under CWE-79 which specifically addresses Cross-Site Scripting vulnerabilities, and represents a classic example of how protocol handler implementations can create security gateways for attacker-controlled code execution. The vulnerability is particularly concerning because it leverages the inherent trust relationships between browsers and protocol handlers, allowing attackers to exploit the normal operation of embedded content loading mechanisms.
The technical exploitation of this vulnerability occurs when Internet Explorer encounters a crafted EMBED element that references MHTML content through a malicious MIME format request. The protocol handler fails to properly validate or sanitize the MIME headers and content parameters, allowing attacker-controlled data to be interpreted as legitimate embedded content. When a victim visits a web page containing such a crafted EMBED element, the browser's MHTML handler processes the request without adequate security checks, leading to script execution in the context of the victim's browsing session. This creates a persistent threat vector that can be used to steal session cookies, perform unauthorized actions on behalf of users, or redirect victims to malicious sites. The vulnerability demonstrates how MIME type handling can become a security boundary failure, where the browser's protocol handler implementation does not adequately separate trusted and untrusted content streams. Attackers can leverage this to bypass security restrictions that normally protect against cross-site scripting attacks, as the malicious content is processed through the legitimate browser protocol handling mechanisms rather than directly through script injection techniques.
The operational impact of this vulnerability extends beyond simple XSS exploitation to encompass significant threats to user security and system integrity. The attack surface is broad due to the widespread deployment of affected Windows versions, making it particularly dangerous in enterprise environments where users may be accessing untrusted web content. Successful exploitation can lead to complete session hijacking, data theft, privilege escalation, and potential lateral movement within networks where users have elevated privileges. The vulnerability's persistence across multiple Windows versions indicates a fundamental flaw in how Microsoft implemented MHTML protocol handling that was not adequately addressed through patching mechanisms. Security professionals must consider this vulnerability as part of broader threat modeling exercises, particularly in environments where users may encounter untrusted web content or where legacy systems remain operational. The impact is particularly severe because it requires no user interaction beyond visiting a malicious webpage, making it a prime candidate for automated exploitation campaigns and social engineering attacks.
Mitigation strategies for CVE-2011-1894 must address both immediate protection and long-term remediation. Organizations should implement comprehensive browser security policies that restrict MHTML content handling, including disabling automatic protocol handler execution for potentially dangerous MIME types. Network-based mitigations such as web application firewalls and content filtering systems can help detect and block malicious EMBED elements targeting this vulnerability. Microsoft's official patches for this vulnerability should be deployed immediately across all affected systems, though administrators should note that the vulnerability's nature means that even patched systems may require additional monitoring for potential exploitation attempts. Security teams should implement enhanced logging and monitoring of browser protocol handler activity, particularly around MHTML content requests, to detect potential exploitation attempts. The vulnerability's classification under ATT&CK technique T1203 (Exploitation for Client Execution) highlights the need for endpoint detection and response capabilities that can identify suspicious protocol handler behavior. Additionally, user education programs should emphasize the dangers of visiting untrusted websites and the importance of keeping systems updated, as this vulnerability was ultimately resolved through Microsoft's security updates that addressed the core protocol handling flaw.