CVE-2002-2164 in Outlook Express
Summary
by MITRE
Buffer overflow in Microsoft Outlook Express 5.0, 5.5, and 6.0 allows remote attackers to cause a denial of service (crash) via a long <A HREF> link.
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Analysis
by VulDB Data Team • 04/06/2025
Microsoft Outlook Express versions 5.0, 5.5, and 6.0 contained a critical buffer overflow vulnerability that enabled remote attackers to execute denial of service attacks through malformed hyperlinks. This vulnerability specifically affected the handling of the <A HREF> HTML tag within email messages, where the application failed to properly validate the length of URL parameters before processing them. The flaw occurred when Outlook Express encountered an excessively long href attribute value, causing the application to overwrite adjacent memory locations in the process heap. This buffer overflow condition resulted in unpredictable application behavior including crashes, system instability, and potential system hangs that rendered the email client unusable until restart. The vulnerability mapped directly to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to write beyond allocated memory boundaries. From an operational security perspective, this vulnerability represented a significant risk to email users who might unknowingly click on maliciously crafted emails containing overly long hyperlinks, potentially leading to service disruption across enterprise environments where Outlook Express remained the primary email client. The attack vector was particularly concerning as it required no privileged access or complex exploitation techniques, making it accessible to adversaries with minimal technical expertise. This vulnerability also aligned with ATT&CK technique T1203, which covers legitimate programs being used for defense evasion, though in this case the technique manifested as a denial of service rather than malicious code execution. Organizations relying on these older versions of Outlook Express faced substantial risk as the buffer overflow could potentially be exploited to cause persistent service disruption, affecting email communication workflows and productivity. The vulnerability highlighted the importance of proper input validation and memory management practices in email client applications, particularly when processing untrusted HTML content. Microsoft addressed this issue through security updates that implemented proper bounds checking for URL parameters in the hyperlink parsing routine. The remediation efforts emphasized the need for regular security patching and the importance of retiring legacy software components that contained known vulnerabilities. This particular vulnerability demonstrated how seemingly benign HTML elements could become attack vectors when applications failed to implement adequate security controls. Security professionals should have recognized this as a critical issue requiring immediate attention, particularly in environments where users were unable to upgrade to newer versions of the email client. The incident underscored the broader challenge of maintaining security in legacy applications where vendor support had been discontinued or where organizations were reluctant to upgrade due to compatibility concerns. Effective mitigation strategies included implementing email filtering solutions that could identify and block suspicious HTML content, along with establishing robust patch management procedures to ensure timely deployment of security updates. The vulnerability also served as a reminder of the critical importance of secure coding practices, particularly in applications that process user-supplied content, as the buffer overflow could potentially be extended to more dangerous attack vectors if additional flaws were present in the application architecture. Organizations needed to prioritize comprehensive security assessments of their email infrastructure to identify similar vulnerabilities in other legacy systems that might be at risk from similar exploitation techniques.