CVE-2004-0844 in Internet Explorer
Summary
by MITRE
Internet Explorer 6 on Double Byte Character Set (DBCS) systems allows remote attackers to alter displayed address bars and spoof web pages via a URL containing special characters, facilitating phishing attacks, aka the "Address Bar Spoofing on Double Byte Character Set Systems Vulnerability."
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Analysis
by VulDB Data Team • 01/02/2025
This vulnerability exists in Internet Explorer 6 when running on systems that utilize Double Byte Character Set encoding, specifically affecting Asian language systems that use character encodings such as Shift-JIS, GB2312, or Big5. The flaw stems from how Internet Explorer processes and displays URLs containing special characters in DBCS environments, creating a fundamental parsing inconsistency between the actual URL structure and its visual representation in the address bar. The vulnerability is categorized under CWE-20 as "Improper Input Validation" and relates to CWE-601 as "URL Redirection to Untrusted Site", making it a prime target for phishing attacks where malicious actors can manipulate the visual presentation of web addresses to deceive users. The issue occurs because the browser's URL parsing algorithm fails to properly handle multibyte character sequences during address bar rendering, allowing attackers to craft URLs that appear legitimate when displayed but actually redirect to malicious sites.
The technical exploitation mechanism involves constructing URLs with specific combinations of DBCS characters that, when processed by Internet Explorer 6, create visual deception in the address bar display. Attackers can manipulate the URL encoding to make the address bar show a trusted domain name while the actual URL contains malicious components. This misrepresentation occurs due to how the browser's rendering engine handles character set conversion between the internal URL representation and the visual display, creating a discrepancy that can be exploited to hide the true destination of web navigation. The vulnerability specifically affects systems where the operating system locale is configured for DBCS character sets, which includes most Japanese, Chinese, and Korean language systems, making it particularly dangerous in regions where these languages are predominant. The attack vector relies on the browser's failure to properly validate and sanitize URL components during the display process, creating a trust boundary violation that can be leveraged for credential theft and other malicious activities.
The operational impact of this vulnerability extends beyond simple phishing attacks to potentially enable more sophisticated social engineering campaigns that can bypass user security awareness. Users navigating DBCS systems may be deceived into believing they are visiting legitimate websites while actually being directed to malicious pages that can harvest credentials, install malware, or conduct other harmful activities. The vulnerability creates a persistent risk because it affects the fundamental user interface element that users rely upon for verifying website authenticity, effectively undermining the security model of web browsing on affected systems. Organizations with users on DBCS systems face increased risk of successful phishing attacks, particularly in financial services, government agencies, and other sectors where credential security is paramount. This vulnerability also demonstrates the challenges of implementing secure web browsers in internationalized environments where character encoding standards vary significantly from standard ASCII-based systems. The issue represents a classic example of how internationalization and localization features can introduce security vulnerabilities when not properly implemented with security considerations in mind.
Mitigation strategies for this vulnerability include immediate deployment of Microsoft security patches that address the URL parsing and display inconsistencies in Internet Explorer 6, along with browser updates to more recent versions that have resolved these DBCS handling issues. Organizations should implement additional security measures such as URL filtering systems, browser hardening configurations, and user education programs that specifically address the risks of address bar spoofing. Network-level protections such as web application firewalls and content filtering solutions can help detect and block suspicious URL patterns that may exploit this vulnerability. Security teams should also consider implementing browser security policies that disable or restrict DBCS character handling in web browsers where such features are not essential for business operations. The vulnerability highlights the importance of comprehensive security testing across different international character sets and locales, and organizations should establish security review processes that consider how internationalization features might impact overall system security. Regular security assessments should include testing of web browser behavior in various locale settings to identify similar vulnerabilities that might exist in other character encoding scenarios.