CVE-2015-6138 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 8 through 11 mishandles HTML attributes in HTTP responses, which allows remote attackers to bypass a cross-site scripting (XSS) protection mechanism via unspecified vectors, aka "Internet Explorer XSS Filter Bypass Vulnerability."
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Analysis
by VulDB Data Team • 06/28/2022
The CVE-2015-6138 vulnerability represents a critical cross-site scripting protection mechanism bypass in Microsoft Internet Explorer versions 8 through 11. This flaw specifically targets the browser's built-in XSS filter that is designed to prevent malicious scripts from being executed when users navigate to potentially compromised web pages. The vulnerability arises from how Internet Explorer processes and interprets HTML attributes within HTTP response headers, creating an unexpected pathway for attackers to circumvent the security protections that should otherwise neutralize malicious payloads. The issue stems from the browser's failure to properly validate or sanitize HTML attributes that are processed during the rendering of web content, allowing attackers to craft malicious responses that appear legitimate to the browser's security mechanisms.
This technical flaw operates at the intersection of web browser security architecture and HTTP protocol handling, where the XSS filter's logic fails to account for specific patterns in HTML attribute processing that can be manipulated by remote attackers. The vulnerability's impact is particularly severe because it undermines the fundamental security model that browsers employ to protect users from malicious scripts, essentially allowing attackers to bypass client-side security controls that are meant to be automatically enforced. The unspecified vectors mentioned in the description suggest that the bypass can occur through multiple attack pathways, making the vulnerability more challenging to defend against and more broadly exploitable across different web application contexts.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to perform a wide range of malicious activities including session hijacking, credential theft, and data exfiltration. When successful, the bypass allows attackers to inject malicious scripts that can access user sessions, steal cookies, redirect users to malicious sites, or even perform actions on behalf of authenticated users. This represents a significant threat to user privacy and web security, particularly in enterprise environments where Internet Explorer remains in use. The vulnerability's persistence across multiple versions of Internet Explorer indicates a systemic issue in how the browser's security mechanisms handle HTML attribute processing, suggesting that the flaw exists in the core architectural components rather than being a simple patchable code issue.
From a security standards perspective, this vulnerability aligns with CWE-79 which describes Cross-Site Scripting flaws, and demonstrates characteristics consistent with ATT&CK technique T1059.001 for command and scripting interpreter and T1566 for credential access. The bypass mechanism specifically relates to the browser's content security policies and its handling of untrusted input, which should normally be filtered by the XSS protection layer. Organizations affected by this vulnerability must implement immediate mitigations including browser updates, enhanced web application security controls, and user education about the risks of visiting untrusted websites. The vulnerability also highlights the importance of maintaining up-to-date browser security mechanisms and the inherent risks of relying solely on client-side protections without proper server-side validation and sanitization of web content.