CVE-2006-0585 in Internet Explorer
Summary
by MITRE
jscript.dll in Microsoft Internet Explorer 6.0 SP1 and earlier allows remote attackers to cause a denial of service (application crash) via a Shockwave Flash object that contains ActionScript code that calls VBScript, which in turn calls the Javascript document.write function, which triggers a null dereference.
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Analysis
by VulDB Data Team • 05/07/2019
The vulnerability described in CVE-2006-0585 represents a critical denial of service flaw affecting Microsoft Internet Explorer 6.0 Service Pack 1 and earlier versions. This issue specifically targets the jscript.dll component within the browser's scripting engine, creating a chain of execution that leads to application instability. The vulnerability manifests when Internet Explorer processes Shockwave Flash objects containing ActionScript code that invokes VBScript functions, which subsequently attempt to call the JavaScript document.write function. This complex interaction creates a scenario where the browser's JavaScript engine encounters a null pointer dereference, resulting in an immediate application crash that terminates the browser session.
The technical root cause of this vulnerability lies in the improper handling of cross-scripting calls between different scripting engines within Internet Explorer. When ActionScript code triggers VBScript execution, and that VBScript code attempts to invoke JavaScript functionality through document.write, the system fails to properly validate memory references. This null dereference occurs because the JavaScript engine does not adequately check for null pointers before attempting to access memory locations, leading to an unhandled exception that crashes the entire browser process. The vulnerability operates at the intersection of multiple scripting technologies and demonstrates poor memory management practices within the browser's engine architecture. According to CWE-476, this represents a NULL Pointer Dereference vulnerability where the application attempts to access memory through a null pointer reference, which is a common class of software defects that can lead to system instability.
From an operational perspective, this vulnerability poses significant risks to users who may encounter malicious Flash content while browsing the web. Attackers can craft specially designed Shockwave Flash files that trigger this specific chain of execution, causing unexpected browser crashes that disrupt user productivity and potentially provide opportunities for more sophisticated attacks. The denial of service impact extends beyond simple browser termination, as users may lose unsaved work and be forced to restart their browsing sessions. This vulnerability is particularly dangerous in enterprise environments where browser stability is critical for business operations, as it can be exploited to disrupt normal workflow and productivity. The attack vector is relatively simple to implement, requiring only the creation of malicious Flash content that follows the specific execution path described in the vulnerability.
Security professionals should implement multiple layers of defense to mitigate this vulnerability effectively. The primary recommendation involves applying the Microsoft security patch released for this specific issue, which addresses the underlying null pointer dereference in the jscript.dll component. Additionally, organizations should consider implementing browser hardening measures such as disabling ActiveX controls and restricting Flash content execution in web browsers. Network-level protections can include content filtering solutions that identify and block malicious Flash content before it reaches end-user systems. According to ATT&CK framework tactic TA0005 (Defense Evasion) and technique T1059.007 (Scripting), this vulnerability represents a classic example of script-based exploitation where attackers leverage legitimate scripting capabilities to execute malicious code that bypasses traditional security controls. Organizations should also consider implementing application whitelisting policies that restrict execution of potentially vulnerable scripting components, particularly in environments where legacy browsers must be maintained for compatibility reasons. The vulnerability highlights the importance of comprehensive testing across multiple scripting engine interactions and the need for robust memory validation practices in complex software systems.