CVE-2004-2011 in Internet Explorer
Summary
by MITRE
msxml3.dll in Internet Explorer 6.0.2600.0 allows remote attackers to cause a denial of service (crash) via a single & (ampersand) in a <Ref href> link, which triggers a parsing error, possibly due to missing portions of the URI.
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Analysis
by VulDB Data Team • 05/07/2019
The vulnerability described in CVE-2004-2011 represents a classic denial of service flaw affecting Microsoft Internet Explorer 6.0.2600.0 through the msxml3.dll component responsible for XML parsing operations. This issue manifests when Internet Explorer encounters a malformed XML reference link containing only a single ampersand character within the href attribute of a <Ref> element. The vulnerability operates at the parsing layer where the XML processor fails to properly handle this specific malformed input, leading to a complete application crash and subsequent denial of service condition for the affected user.
The technical root cause of this vulnerability lies in the insufficient input validation and error handling mechanisms within the msxml3.dll library. When Internet Explorer processes XML content containing the malformed reference, the parsing routine encounters an unexpected sequence that triggers an unhandled exception or memory corruption state. This parsing error occurs specifically within the URI handling logic where the single ampersand character fails to constitute a valid URI fragment, causing the XML parser to either enter an infinite loop, access invalid memory locations, or otherwise corrupt the application's execution state. The vulnerability demonstrates a weakness in the XML processing pipeline that lacks proper bounds checking and error recovery mechanisms.
From an operational impact perspective, this vulnerability presents a significant security concern as it allows remote attackers to execute denial of service attacks against targeted systems without requiring any special privileges or authentication. The attack vector is particularly dangerous because it can be delivered through standard web content, making it easily exploitable through malicious websites, email attachments, or compromised web pages. When successfully exploited, the vulnerability results in a complete browser crash, forcing users to restart their browsing session and potentially disrupting business operations. The vulnerability affects the core functionality of Internet Explorer, making it a critical issue for organizations relying on this browser for business operations.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. The primary recommendation involves applying the official Microsoft security update that patches the msxml3.dll component and corrects the XML parsing error handling. Additionally, network administrators should consider implementing web content filtering solutions that can identify and block malformed XML content before it reaches end-user browsers. Browser configuration settings can be adjusted to disable automatic XML processing or to enforce stricter parsing rules for XML content. From a defensive standpoint, this vulnerability aligns with CWE-129, which describes improper validation of array indices, and represents a classic example of CWE-248, indicating an exception not caught by the application. The attack pattern corresponds to techniques described in the ATT&CK framework under T1499, specifically targeting the availability of applications through denial of service mechanisms. Organizations should also consider implementing network segmentation and monitoring solutions to detect unusual patterns of service disruption that might indicate exploitation attempts.