CVE-2008-5424 in Outlook Express
Summary
by MITRE
The MimeOleClearDirtyTree function in InetComm.dll in Microsoft Outlook Express 6.00.2900.5512 does not properly handle (1) multipart/mixed e-mail messages with many MIME parts and possibly (2) e-mail messages with many "Content-type: message/rfc822;" headers, which allows remote attackers to cause a denial of service (infinite loop) via a large e-mail message, a related issue to CVE-2006-1173.
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Analysis
by VulDB Data Team • 11/27/2017
The vulnerability described in CVE-2008-5424 represents a classic denial of service flaw affecting Microsoft Outlook Express 6.00.2900.5512 through improper handling of complex MIME email structures. This issue resides within the MimeOleClearDirtyTree function located in the InetComm.dll component, which is responsible for processing and managing email message structures. The flaw manifests when processing multipart/mixed email messages containing an excessive number of MIME parts or emails with numerous "Content-type: message/rfc822;" headers, creating a condition where the processing logic becomes trapped in an infinite loop.
The technical implementation of this vulnerability stems from inadequate input validation and boundary checking within the email parsing routine. When Outlook Express encounters email messages with excessive MIME component nesting or repetitive message/rfc822 content types, the MimeOleClearDirtyTree function fails to properly terminate its recursive processing operations. This function is designed to clear dirty tree flags during MIME structure processing, but when faced with maliciously crafted messages containing thousands of nested components, it enters an infinite loop where it repeatedly processes the same structures without proper exit conditions. The vulnerability specifically relates to CWE-835, which addresses infinite loops in software, and falls under the broader category of improper input validation issues.
From an operational perspective, this vulnerability creates significant disruption for email clients running affected versions of Outlook Express. Attackers can exploit this weakness by crafting specially formatted email messages that trigger the infinite loop condition, causing the application to consume excessive CPU resources and become unresponsive. The denial of service impact extends beyond individual user experience to potentially affect entire email servers or client systems if multiple users are simultaneously targeted. The related nature of this vulnerability to CVE-2006-1173 indicates a pattern of similar processing flaws in Microsoft's email handling components, suggesting systemic issues in how the software manages complex email structures.
The exploitation of this vulnerability aligns with ATT&CK technique T1499.004, which covers "Domain Name System (DNS) Server Deception" and related denial of service tactics. Organizations using affected Outlook Express versions face potential operational risks including email service degradation, application crashes, and resource exhaustion that could impact business continuity. Network administrators should consider implementing email filtering rules to identify and block emails with suspiciously high MIME part counts or excessive message/rfc822 headers. The vulnerability demonstrates the importance of proper resource management in email processing applications and highlights the need for robust input validation mechanisms. Microsoft addressed this issue through security updates and patches, but organizations should ensure all affected systems receive proper remediation. The flaw also underscores the critical need for email client software to implement proper loop detection and termination mechanisms when processing potentially malformed or malicious email content.