CVE-2008-5554 in Internet Explorer
Summary
by MITRE
The XSS Filter in Microsoft Internet Explorer 8.0 Beta 2 does not properly handle some HTTP headers that appear after a CRLF sequence in a URI, which allows remote attackers to bypass the XSS protection mechanism and conduct XSS or redirection attacks, as demonstrated by the (1) Location and (2) Set-Cookie HTTP headers. NOTE: the vendor has reportedly stated that the XSS Filter intentionally does not attempt to "address every conceivable XSS attack scenario."
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Analysis
by VulDB Data Team • 08/03/2021
The vulnerability described in CVE-2008-5554 represents a critical flaw in Microsoft Internet Explorer 8.0 Beta 2's cross-site scripting protection mechanism, specifically targeting the XSS Filter component that was introduced as part of the browser's security enhancements. This weakness exploits a fundamental parsing issue within the browser's handling of HTTP headers, particularly when these headers appear after a carriage return line feed sequence within Uniform Resource Identifier structures. The vulnerability demonstrates how even sophisticated security measures can be circumvented through careful manipulation of input parsing behavior, exposing users to potential malicious code execution and unauthorized redirection attacks.
The technical implementation of this flaw occurs when Internet Explorer encounters HTTP headers that are positioned after a CRLF sequence within a URI structure. The XSS Filter in IE8 fails to properly process these headers, particularly the Location and Set-Cookie headers, which allows attackers to inject malicious content that bypasses the intended security protections. This parsing inconsistency creates a scenario where the browser's security mechanisms are effectively circumvented, enabling attackers to execute cross-site scripting payloads or redirect users to malicious websites without triggering the browser's warning mechanisms. The vulnerability specifically leverages the way the browser processes header information, where the presence of CRLF sequences disrupts the expected parsing flow and allows malicious content to be interpreted as legitimate.
From an operational standpoint, this vulnerability presents significant risk to users of the affected browser version, as it allows attackers to bypass one of the primary defenses against cross-site scripting attacks. The ability to conduct XSS attacks through Location and Set-Cookie headers means that attackers can manipulate browser behavior in multiple ways, including injecting malicious scripts that can steal session cookies, redirect users to phishing sites, or execute unauthorized commands within the browser context. The vulnerability's impact extends beyond simple script injection to include potential session hijacking and credential theft, as the Set-Cookie header manipulation can be used to establish malicious cookies that persist across user sessions. This represents a particularly dangerous scenario because the XSS Filter's failure to properly handle these headers occurs at the protocol level, making it difficult for users to detect or prevent the attacks.
The security implications of this vulnerability align with CWE-79, which describes Cross-Site Scripting flaws in web applications, and demonstrates how browser-based protections can be undermined by parsing inconsistencies in HTTP header handling. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communication, credential access, and privilege escalation through browser-based attacks. The vendor's acknowledgment that the XSS Filter intentionally does not address every conceivable scenario highlights the inherent challenges in creating comprehensive security solutions for complex web protocols, where the sheer number of potential attack vectors makes complete protection practically impossible. Organizations should consider this vulnerability as part of a broader strategy for browser security management, including regular updates, network monitoring, and user education about the risks of visiting untrusted websites or clicking suspicious links. The vulnerability also underscores the importance of maintaining up-to-date security patches and the potential risks associated with using beta software versions that may contain undiscovered security flaws.