CVE-2011-1962 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 through 9 does not properly handle unspecified character sequences, which allows remote attackers to read content from a different (1) domain or (2) zone via a crafted web site that triggers "inactive filtering," aka "Shift JIS Character Encoding Vulnerability."
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Analysis
by VulDB Data Team • 11/17/2021
The CVE-2011-1962 vulnerability represents a critical character encoding flaw in Microsoft Internet Explorer versions 6 through 9 that fundamentally undermines web browser security boundaries. This vulnerability operates through a sophisticated manipulation of Shift JIS character encoding standards, exploiting how the browser processes multibyte character sequences that fall outside of standard ASCII ranges. The flaw specifically targets the browser's handling of unspecified character sequences within the Shift JIS encoding scheme, creating a pathway for malicious actors to bypass security restrictions that normally separate different domains and security zones.
The technical mechanism behind this vulnerability involves the improper processing of Shift JIS encoded characters that contain embedded null bytes or other control sequences. When Internet Explorer encounters these malformed character sequences, it fails to properly validate the encoding boundaries, allowing it to interpret certain byte patterns as valid content from different domains or security zones. This creates what cybersecurity experts term an "inactive filtering" condition where the browser's security mechanisms become ineffective, enabling cross-domain data access that should be strictly prohibited. The vulnerability is particularly dangerous because it leverages the legitimate character encoding support that Internet Explorer provides while exploiting implementation gaps in how these encodings are processed.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it creates a fundamental breach in web browser security architecture that can be exploited for various malicious activities. Attackers can craft malicious websites that appear legitimate to users while silently accessing content from other domains, potentially including sensitive corporate data, personal information, or authentication tokens. This cross-domain access capability can be weaponized for session hijacking, credential theft, or data exfiltration attacks. The vulnerability affects all versions of Internet Explorer from version 6 through 9, representing a broad attack surface that was particularly concerning given the widespread deployment of these older browser versions in enterprise environments. The impact is exacerbated by the fact that many organizations continued to use these legacy browsers well beyond their support lifecycle, creating extended exposure windows for exploitation.
Mitigation strategies for CVE-2011-1962 require a multi-layered approach that addresses both immediate security concerns and long-term architectural improvements. Organizations should prioritize immediate browser updates to the latest supported versions of Internet Explorer or migration to modern browser platforms that have addressed this vulnerability. Network-level protections such as content filtering systems and web application firewalls can help detect and block malicious character sequences, though these solutions may not prevent all exploitation attempts. Security configuration hardening of Internet Explorer should include disabling support for problematic character encodings where possible, implementing strict security zone policies, and enabling enhanced protection mechanisms. From a compliance perspective, this vulnerability aligns with CWE-134 which addresses format string vulnerabilities and reflects patterns identified in the ATT&CK framework under technique T1189 for additional execution prevention. The vulnerability also demonstrates the importance of proper input validation and encoding handling in web applications, as similar issues have been observed in other software components and highlight the critical need for robust character encoding security practices in web development.