CVE-1999-0876 in Internet Explorer
Summary
by MITRE
Buffer overflow in Internet Explorer 4.0 via EMBED tag.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability identified as CVE-1999-0876 represents a critical buffer overflow flaw discovered in Internet Explorer 4.0 through its handling of the EMBED tag within html documents. This vulnerability stems from insufficient bounds checking in the browser's processing of embedded objects, specifically when the EMBED tag contains overly long data strings that exceed the allocated buffer space. The flaw exists at the application level where the browser fails to validate input lengths before copying data into fixed-size memory buffers, creating an exploitable condition that can be leveraged by malicious actors to execute arbitrary code on vulnerable systems.
The technical implementation of this vulnerability occurs when Internet Explorer encounters an EMBED tag with malformed or excessively long parameters that surpass the predefined buffer limits. According to CWE-121, this represents a classic stack-based buffer overflow condition where the overflow occurs in the stack memory region. The vulnerability manifests when the browser's rendering engine processes embedded content and attempts to store user-supplied data into a fixed-length buffer without proper size validation. This allows an attacker to overwrite adjacent memory locations including return addresses, function pointers, and other critical program state information. The ATT&CK framework categorizes this as a code injection technique under T1059 where adversaries leverage application vulnerabilities to execute malicious code.
The operational impact of CVE-1999-0876 is severe and far-reaching given the widespread adoption of Internet Explorer 4.0 during the late 1990s. When exploited, this vulnerability enables remote code execution with the privileges of the user running the browser, potentially allowing attackers to gain full system control. The attack vector is particularly dangerous because it can be delivered through standard web browsing activities without requiring any special privileges or user interaction beyond visiting a malicious website. The vulnerability affects not only individual users but also enterprise environments where the browser is commonly used for business applications and internal web portals. Additionally, the exploitation can lead to complete system compromise including data theft, privilege escalation, and installation of persistent backdoors.
Mitigation strategies for this vulnerability focus on both immediate patching and defensive measures. Microsoft released security updates to address this specific buffer overflow condition in subsequent versions of Internet Explorer, emphasizing the importance of keeping browsers current with security patches. Organizations should implement network-based protections such as web application firewalls that can detect and block malformed EMBED tags with suspicious parameter lengths. Browser security configurations should be hardened by disabling unnecessary embedded object processing or implementing strict content filtering policies. From a defensive standpoint, users should be educated about avoiding untrusted websites and suspicious web content. The vulnerability also highlights the need for proper input validation and bounds checking in software development practices, aligning with secure coding guidelines that prevent similar issues in future applications. System administrators should monitor for exploitation attempts through network logs and implement intrusion detection systems capable of identifying buffer overflow patterns in web traffic.