CVE-2015-6176 in Edge
Summary
by MITRE
Microsoft Edge mishandles HTML attributes in HTTP responses, which allows remote attackers to bypass a cross-site scripting (XSS) protection mechanism via unspecified vectors, aka "Microsoft Edge XSS Filter Bypass Vulnerability."
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Analysis
by VulDB Data Team • 07/24/2025
The vulnerability identified as CVE-2015-6176 represents a critical security flaw in Microsoft Edge browser's handling of HTML attributes within HTTP responses. This issue specifically targets the browser's cross-site scripting protection mechanisms, creating a scenario where malicious actors can circumvent intended security controls. The vulnerability stems from improper parsing or validation of HTML attributes that are received in HTTP response content, allowing attackers to craft payloads that evade the browser's built-in XSS filtering capabilities. Such a bypass fundamentally undermines the security model that browsers implement to protect users from malicious script execution, particularly in web applications that rely on dynamic content delivery.
The technical implementation of this vulnerability involves Microsoft Edge's insufficient validation of HTML attributes during the parsing of HTTP responses. When the browser processes web content that contains potentially malicious attributes within HTML elements, it fails to properly sanitize or validate these attributes against known XSS attack patterns. This parsing flaw creates opportunities for attackers to inject script code that appears benign to the browser's security filters but can execute malicious actions when rendered in the user's browser context. The unspecified vectors mentioned in the description suggest that multiple attack paths exist, potentially including various attribute types, content encoding methods, or response format variations that can trigger the bypass condition.
The operational impact of this vulnerability extends beyond simple script execution, as it compromises the fundamental security assumptions that web applications and users rely upon. When an attacker successfully bypasses the XSS filter, they can inject malicious scripts that can steal session cookies, redirect users to phishing sites, modify page content, or perform actions on behalf of the authenticated user. This represents a significant risk in environments where users interact with untrusted web content, as the vulnerability can be exploited through various attack vectors including email links, malicious advertisements, or compromised websites. The implications are particularly severe given that Microsoft Edge was designed with enhanced security features, making the bypass of its XSS protection mechanisms a notable weakness in the browser's security architecture.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate browser-level issue and broader security practices. Organizations should implement the latest security updates from Microsoft that contain patches for this vulnerability, as the fix typically involves enhanced HTML attribute validation and improved XSS filter logic. Additionally, web application developers should employ comprehensive input validation, output encoding, and Content Security Policy implementations to provide defense-in-depth against potential exploitation attempts. The vulnerability aligns with CWE-79 which describes Cross-site Scripting flaws, and can be mapped to ATT&CK technique T1203 which covers Exploitation for Client Execution, highlighting the attack surface that allows for remote code execution through browser-based vulnerabilities. Security teams should also consider implementing network-level protections such as web application firewalls and monitoring for suspicious attribute patterns in HTTP responses to detect potential exploitation attempts.