CVE-2004-0549 in Internet Explorer
Summary
by MITRE
The WebBrowser ActiveX control, or the Internet Explorer HTML rendering engine (MSHTML), as used in Internet Explorer 6, allows remote attackers to execute arbitrary code in the Local Security context by using the showModalDialog method and modifying the location to execute code such as Javascript, as demonstrated using (1) delayed HTTP redirect operations, and an HTTP response with a Location: header containing a "URL:" prepended to a "ms-its" protocol URI, or (2) modifying the location attribute of the window, as exploited by the Download.ject (aka Scob aka Toofer) using the ADODB.Stream object.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability described in CVE-2004-0549 represents a critical security flaw in Internet Explorer 6's WebBrowser ActiveX control and MSHTML rendering engine that enables remote code execution with local security privileges. This vulnerability specifically targets the showModalDialog method implementation within the browser's HTML rendering engine, creating an exploitable condition that allows attackers to execute arbitrary code in the context of the local security zone. The flaw arises from insufficient validation of URI protocols and location modifications within the browser's dialog handling mechanisms, effectively bypassing security restrictions that should prevent cross-zone code execution.
The technical exploitation mechanism leverages two primary approaches that demonstrate the breadth of the vulnerability's impact. The first method involves utilizing delayed HTTP redirect operations combined with specially crafted HTTP responses containing Location headers with "URL:" prepended to "ms-its" protocol URIs. This technique exploits how Internet Explorer processes these specific URI formats within the showModalDialog context, allowing JavaScript execution within the local security context. The second approach modifies the location attribute of the window object using the ADODB.Stream object, as demonstrated by the Download.ject (also known as Scob or Toofer) malware family. This alternative exploitation vector demonstrates how the vulnerability can be triggered through different code paths within the same underlying flaw, making it particularly dangerous and difficult to defend against completely.
The operational impact of this vulnerability is severe as it enables attackers to execute malicious code with local security privileges, potentially allowing them to access sensitive user data, modify system files, or establish persistent backdoors. The Local Security context provides elevated permissions compared to the Internet zone, meaning that successful exploitation could result in complete system compromise. The vulnerability affects Internet Explorer 6 specifically, which was widely deployed in corporate and enterprise environments during that time period, making it particularly attractive to attackers targeting these environments. The exploit techniques described in the vulnerability are relatively sophisticated and require knowledge of browser internals, but they are effective against a significant portion of the user base at the time of discovery.
The underlying technical flaw can be categorized under CWE-117, which describes improper output neutralization for logs, and CWE-79, which covers cross-site scripting vulnerabilities, though the specific implementation details are more closely aligned with improper input validation in ActiveX controls. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 for script-based execution and T1068 for local privilege escalation. The attack surface is particularly concerning because it operates at the browser engine level, making it difficult to detect through traditional network-based security measures. The exploitation requires minimal user interaction beyond visiting a malicious website or opening a malicious document, which makes it particularly dangerous in phishing campaigns or drive-by download scenarios.
Mitigation strategies for this vulnerability should include immediate patching of Internet Explorer 6 to the latest available security updates from Microsoft, which would address the underlying implementation flaw in the WebBrowser ActiveX control and MSHTML rendering engine. Organizations should also implement browser hardening measures such as disabling ActiveX controls where possible, implementing strict security policies for the local zone, and using security software that can detect and block malicious URL patterns. Network-based defenses can include filtering HTTP headers to prevent the specific "URL:" prepended "ms-its" protocol combinations, though this approach may impact legitimate functionality. Additionally, users should be educated about the risks of visiting untrusted websites and opening suspicious attachments, as social engineering remains a critical component of exploitation for this type of vulnerability. The vulnerability highlights the importance of keeping browser software up to date and implementing defense-in-depth strategies to protect against similar flaws in other browser components.