CVE-2008-4787 in Internet Explorer
Summary
by MITRE
Visual truncation vulnerability in Microsoft Internet Explorer 6 allows remote attackers to spoof the address bar via a URL with a hostname containing many (Non-Blocking Space character) sequences, which are rendered as whitespace, aka MSRC ticket MSRC7899, a related issue to CVE-2003-1025.
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Analysis
by VulDB Data Team • 08/04/2025
The vulnerability described in CVE-2008-4787 represents a sophisticated visual spoofing attack targeting Microsoft Internet Explorer 6 through a specific rendering flaw in the browser's address bar display mechanism. This issue exploits the way Internet Explorer processes and renders HTML entities, particularly the non-breaking space character sequence which when repeated excessively in URL hostnames can manipulate the visual presentation of web addresses. The vulnerability operates by leveraging the browser's inability to properly handle excessive whitespace characters within URL components, creating a deceptive visual environment that can mislead users about the true destination of web links. The attack vector specifically targets the address bar display where users expect to see the actual website address, but instead observe a manipulated presentation that may appear to be a legitimate domain while actually pointing to malicious content. This visual truncation technique creates a security risk because users may be deceived into trusting addresses that appear legitimate but actually lead to fraudulent or malicious websites.
The technical flaw stems from the browser's HTML parsing and rendering engine's handling of whitespace characters within URL hostnames. When Internet Explorer 6 encounters a URL containing numerous consecutive character sequences in the hostname portion, the browser's rendering process treats these as visible whitespace characters that can cause the address bar to truncate or display the URL in a manner that obscures the actual domain. This behavior creates a scenario where an attacker can craft a URL that appears to contain a trusted domain name when displayed in the address bar, while the underlying URL may contain different or malicious components. The vulnerability is particularly concerning because it operates at the presentation layer rather than the protocol level, making it difficult to detect through traditional network monitoring or security scanning tools. The flaw demonstrates a classic case of improper input validation and output encoding where the browser fails to properly sanitize or normalize URL components before displaying them to users.
The operational impact of this vulnerability extends beyond simple address bar deception to encompass broader security implications for user trust and website authentication. When users encounter manipulated address bar displays, they may inadvertently trust websites that appear legitimate but are actually malicious, potentially leading to credential theft, malware downloads, or financial fraud. This vulnerability particularly affects users of Internet Explorer 6, which was widely deployed in enterprise environments and among users who had not upgraded to newer browser versions. The attack can be executed remotely through web pages that contain the maliciously crafted URLs, requiring no local exploitation or user interaction beyond visiting the compromised website. Security professionals should note that this vulnerability operates in a manner consistent with attack patterns documented in the attack tree framework, where visual deception serves as a precursor to more serious security incidents. The impact is amplified in environments where users rely heavily on address bar verification for website authentication, as the deception can bypass traditional security measures that depend on visual confirmation.
Mitigation strategies for CVE-2008-4787 focus on both immediate browser security measures and broader organizational security practices. Users should immediately upgrade from Internet Explorer 6 to supported browser versions that properly handle URL rendering and whitespace characters. Organizations should implement comprehensive browser security policies that mandate regular updates and patch management for all web browsers. Network administrators should consider implementing URL filtering solutions that can detect and block suspicious URL patterns containing excessive whitespace characters. The vulnerability aligns with CWE-174, which addresses improper handling of inputs that may cause unexpected behavior in software systems, and demonstrates the importance of proper input sanitization. From an attack perspective, this vulnerability can be classified under the MITRE ATT&CK framework as a technique for credential access and defense evasion, where visual spoofing serves as both a deception mechanism and a method to bypass security controls. Security teams should also consider implementing user education programs that emphasize the importance of verifying website addresses through multiple means beyond address bar inspection, particularly in environments where legacy browser support is still required. The vulnerability highlights the critical need for robust input validation and output encoding practices in web applications and browser implementations to prevent similar issues from occurring in modern systems.