CVE-1999-0871 in Internet Explorer
Summary
by MITRE
Internet Explorer 4.0 and 4.01 allow a remote attacker to read files via IE's cross frame security, aka the "Cross Frame Navigate" vulnerability.
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Analysis
by VulDB Data Team • 04/17/2026
The CVE-1999-0871 vulnerability represents a critical cross-frame scripting security flaw in Internet Explorer 4.0 and 4.01 versions that fundamentally compromised the browser's security model. This vulnerability specifically exploited the way Internet Explorer handled cross-frame navigation operations, allowing malicious actors to bypass security restrictions that were designed to prevent unauthorized access between different frames within a web page. The flaw emerged from the browser's inadequate enforcement of security boundaries when processing navigation requests that crossed frame boundaries, creating an avenue for attackers to access sensitive information from other frames without proper authorization.
The technical implementation of this vulnerability leveraged the browser's cross-frame navigation capabilities to execute malicious code that could read files from other frames, effectively breaking down the security isolation that should exist between different content sources. When a user visited a malicious web page containing specially crafted cross-frame navigation code, the browser would process the navigation request in a way that allowed the attacker to access resources that were normally restricted. This occurred because the security model failed to properly validate navigation operations that originated from one frame and targeted content within another frame, particularly when the frames were from different security zones or origins.
The operational impact of this vulnerability was severe as it enabled remote attackers to perform unauthorized file access operations across different security contexts within the browser environment. An attacker could construct malicious web pages that would exploit this vulnerability to read local files, access cached data, or retrieve information from other frames that should have been protected by security policies. The vulnerability particularly affected users who had multiple frames loaded in their browser windows, as it allowed attackers to leverage the cross-frame navigation functionality to gain access to resources that were normally protected by the browser's security model. This created a significant risk for users who visited compromised websites, as the vulnerability could be exploited without any user interaction beyond simply visiting the malicious page.
This vulnerability aligns with CWE-94, which describes the weakness of allowing code to be executed in a context where it could be used to bypass security controls. The flaw represents a classic example of inadequate input validation and insufficient access control enforcement within the browser's frame management system. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access, as attackers could leverage the cross-frame navigation to gain unauthorized access to sensitive information. The vulnerability also relates to T1059, which covers execution of malicious code through web-based attack vectors, and T1071, which addresses application layer protocols used for command and control communications.
Mitigation strategies for this vulnerability required immediate patching of the affected Internet Explorer versions, as Microsoft released security updates to address the cross-frame navigation flaw. Organizations needed to implement browser hardening measures, including disabling cross-frame navigation features when not required, and ensuring that users only accessed trusted websites. The vulnerability highlighted the importance of proper security boundary enforcement in web browsers and led to improved security model implementations in subsequent browser versions. Users were advised to avoid visiting untrusted websites and to keep their browsers updated with the latest security patches to prevent exploitation of this and similar cross-frame security vulnerabilities.