CVE-2007-1114 in Internet Explorer
Summary
by MITRE
The child frames in Microsoft Internet Explorer 7 inherit the default charset from the parent window when a charset is not specified in an HTTP Content-Type header or META tag, which allows remote attackers to conduct cross-site scripting (XSS) attacks, as demonstrated using the UTF-7 character set.
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Analysis
by VulDB Data Team • 03/15/2021
This vulnerability resides in Microsoft Internet Explorer 7's handling of character encoding within nested frame structures, representing a critical security flaw that undermines web application security boundaries. The issue manifests when child frames inherit the parent window's default character set without explicit specification, creating an environment where malicious actors can exploit encoding inconsistencies to bypass security controls. The vulnerability specifically leverages the UTF-7 character set as a demonstration vector, highlighting how improper charset handling can enable attackers to inject malicious content that executes in the context of the parent frame's security domain.
The technical flaw stems from Internet Explorer's frame inheritance mechanism where child frames automatically adopt the parent window's character encoding settings when no explicit charset is declared through HTTP headers or HTML meta tags. This inheritance behavior creates a dangerous scenario where an attacker can manipulate the parent frame's charset to UTF-7, a character encoding that allows the representation of Unicode characters through ASCII byte sequences. When the child frame inherits this UTF-7 encoding, it can be exploited to craft XSS payloads that appear benign to the browser's security mechanisms but actually execute malicious code within the parent frame's context.
The operational impact of this vulnerability extends beyond simple cross-site scripting attacks, as it fundamentally compromises the security model that separates different content sources within web browsers. Attackers can construct malicious web pages that, when loaded in a parent frame with UTF-7 encoding, cause child frames to interpret attacker-controlled content as legitimate, thereby bypassing same-origin policy restrictions. This allows for sophisticated attacks where malicious scripts can access cookies, session information, and other sensitive data from the parent frame's context, effectively breaking down the security boundaries that protect user sessions and sensitive information.
This vulnerability aligns with CWE-1004, which addresses insecure default configurations in web applications, and maps to ATT&CK technique T1059.007 for script injection. The flaw represents a classic case of improper input validation and encoding handling that enables attackers to manipulate browser behavior through subtle configuration differences. Organizations using Internet Explorer 7 were particularly vulnerable as the browser's frame inheritance mechanism did not properly validate or override charset settings, creating an attack surface that could be exploited across multiple web applications. The vulnerability demonstrates the critical importance of proper character encoding management in web security and highlights how seemingly minor implementation details can create significant security risks.
Mitigation strategies for this vulnerability required immediate browser updates and proper charset declaration practices in web applications. Microsoft released patches to address the inheritance behavior, while security best practices emphasized the explicit declaration of character encodings in both parent and child frames. Web developers needed to ensure that all HTTP responses included proper Content-Type headers with explicit charset specifications and that HTML documents contained meta tags defining character sets. Additionally, implementing Content Security Policy headers and proper input validation mechanisms helped reduce the attack surface, though the fundamental browser-level fix remained necessary to address the core inheritance flaw that enabled this class of XSS attacks.