CVE-1999-1016 in Internet Explorer
Summary
by MITRE
Microsoft HTML control as used in (1) Internet Explorer 5.0, (2) FrontPage Express, (3) Outlook Express 5, and (4) Eudora, and possibly others, allows remote malicious web site or HTML emails to cause a denial of service (100% CPU consumption) via large HTML form fields such as text inputs in a table cell.
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Analysis
by VulDB Data Team • 01/18/2025
The vulnerability described in CVE-1999-1016 represents a classic denial of service flaw affecting multiple Microsoft products that utilized the HTML control component. This vulnerability specifically impacted Internet Explorer 5.0, FrontPage Express, Outlook Express 5, and Eudora applications, all of which relied on the same underlying HTML rendering engine. The flaw manifested when these applications processed HTML content containing excessively large form fields, particularly text inputs nested within table cells, leading to sustained high CPU utilization that effectively rendered the affected applications unusable.
The technical mechanism behind this vulnerability involves the HTML control's insufficient input validation and memory management when processing malformed HTML content. When the control encountered HTML form fields with extremely large data values, particularly within table cell structures, the parsing and rendering processes would consume excessive computational resources. This behavior aligns with CWE-400, which categorizes uncontrolled resource consumption as a significant security weakness. The vulnerability exploited the control's failure to implement proper bounds checking on input data, allowing malicious actors to craft HTML content that would cause the application to enter an infinite loop or consume disproportionate system resources.
The operational impact of this vulnerability extended beyond simple application crashes, creating a persistent denial of service condition that could affect users' productivity and system availability. Attackers could send malicious HTML emails or host compromised web pages that would trigger the vulnerability when users opened them in affected applications. This vector of attack was particularly dangerous because it could affect users across different Microsoft products that shared the same HTML control component, amplifying the potential impact. The 100% CPU consumption scenario meant that affected systems would become unresponsive, requiring manual intervention to terminate the malicious processes and restore normal operation.
From a threat modeling perspective, this vulnerability demonstrates how seemingly benign HTML parsing functionality could be weaponized for denial of service attacks. The attack pattern aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. Organizations using affected Microsoft applications were particularly vulnerable because the attack could be executed through email or web browsing without requiring any special privileges or complex exploitation techniques. The widespread use of these applications across enterprise and consumer environments meant that a single compromised email or website could potentially affect numerous users simultaneously.
Mitigation strategies for this vulnerability required both immediate and long-term approaches. Immediate solutions included disabling HTML rendering in email clients, implementing web filtering policies to block suspicious content, and applying available patches from Microsoft. Long-term mitigations involved updating to newer versions of affected applications that contained improved HTML parsing logic and input validation mechanisms. The vulnerability highlighted the importance of proper input sanitization and resource management in client-side applications, leading to improved security practices in subsequent software development cycles. Additionally, organizations should have implemented monitoring systems to detect unusual CPU consumption patterns that could indicate exploitation attempts.