CVE-2002-0371 in Internet Explorer
Summary
by MITRE
Buffer overflow in gopher client for Microsoft Internet Explorer 5.1 through 6.0, Proxy Server 2.0, or ISA Server 2000 allows remote attackers to execute arbitrary code via a gopher:// URL that redirects the user to a real or simulated gopher server that sends a long response.
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Analysis
by VulDB Data Team • 09/18/2025
This vulnerability represents a classic buffer overflow flaw in Microsoft Internet Explorer's gopher client implementation that affected versions 5.1 through 6.0 along with Proxy Server 2.0 and ISA Server 2000. The issue stems from inadequate input validation when processing gopher:// URLs, specifically during the handling of server responses that exceed predetermined buffer boundaries. The vulnerability is categorized under CWE-121 as a stack-based buffer overflow, where maliciously crafted gopher server responses can overwrite adjacent memory locations, potentially leading to arbitrary code execution. This flaw exploits the fundamental weakness in how the affected Microsoft products handle network protocol responses without proper boundary checking mechanisms.
The operational impact of this vulnerability is significant as it enables remote attackers to execute arbitrary code on vulnerable systems simply by tricking users into clicking malicious gopher:// URLs. The attack vector leverages the redirect functionality inherent in the gopher protocol where a user is directed to a malicious server that sends an overly long response designed to overflow the allocated buffer space. This technique falls under the ATT&CK framework's T1203 - Exploitation for Client Execution, specifically targeting client-side applications that process network protocol data. The vulnerability is particularly dangerous because it requires no user interaction beyond visiting a malicious website, making it a prime candidate for drive-by download attacks.
The technical exploitation involves crafting a gopher URL that when processed by the vulnerable client triggers the buffer overflow condition. When the client attempts to parse the response from the malicious gopher server, the excessive data overflows the allocated memory buffer, potentially corrupting the stack and allowing an attacker to inject and execute malicious code with the privileges of the user running the vulnerable application. This vulnerability demonstrates the critical importance of input validation and proper memory management in client applications that process network data. The flaw highlights the risks associated with legacy protocol implementations that may not have been designed with modern security considerations in mind.
Mitigation strategies for this vulnerability include immediate patching of affected Microsoft products through official security updates, implementing network-level filtering to block gopher protocol traffic, and educating users about the dangers of clicking untrusted URLs. Organizations should also consider disabling gopher protocol support in web browsers and proxy servers where it is not essential for business operations. The vulnerability underscores the necessity of regular security assessments and the importance of maintaining up-to-date software versions to protect against known exploits. Additionally, implementing proper network segmentation and access controls can limit the potential impact of successful exploitation attempts. This vulnerability serves as a historical example of how protocol-specific implementations can introduce security risks that persist across multiple product versions and require coordinated remediation efforts.