CVE-1999-1189 in Communicator
Summary
by MITRE
Buffer overflow in Netscape Navigator/Communicator 4.7 for Windows 95 and Windows 98 allows remote attackers to cause a denial of service, and possibly execute arbitrary commands, via a long argument after the ? character in a URL that references an .asp, .cgi, .html, or .pl file.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-1189 represents a critical buffer overflow flaw within Netscape Navigator and Communicator versions 4.7 running on Windows 95 and Windows 98 operating systems. This security weakness stems from inadequate input validation mechanisms within the web browser's handling of Uniform Resource Locators that contain script file extensions such as .asp, .cgi, .html, and .pl. The flaw specifically manifests when a URL contains a query string parameter following the question mark character, where the argument length exceeds the allocated buffer space, creating conditions ripe for exploitation.
The technical implementation of this vulnerability involves the browser's failure to properly bounds-check user-supplied input when processing URLs containing script file references. When a maliciously crafted URL with an excessively long argument string is processed, the application's memory management routines overflow the predetermined buffer boundaries, potentially allowing attackers to overwrite adjacent memory locations. This memory corruption can result in unpredictable program behavior, application crashes, and in more severe cases, complete system compromise. The vulnerability operates at the application layer and leverages the inherent trust users place in web browsers when navigating to seemingly benign websites.
From an operational perspective, this vulnerability presents significant risks to users of legacy systems running the affected Netscape software versions. The remote exploitation capability means attackers can craft malicious web pages or manipulate existing websites to deliver payloads that trigger the buffer overflow condition. The potential for arbitrary code execution represents a severe threat level, as it could enable attackers to gain full system control, install malware, or establish persistent backdoors. Additionally, the denial of service aspect can be leveraged to disrupt legitimate web browsing activities and potentially impact business operations that depend on these legacy browser configurations.
The exploitation of CVE-1999-1189 aligns with common attack patterns documented in the ATT&CK framework under the technique of command and control communications, where attackers establish persistent access through compromised systems. This vulnerability also maps to CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, covering stack-based buffer overflow scenarios. Organizations should implement immediate mitigation strategies including patching to the latest available versions of Netscape Navigator or Communicator, implementing network-based filtering to block suspicious URL patterns, and deploying intrusion detection systems to monitor for exploitation attempts. The vulnerability underscores the importance of proper input validation and memory safety practices in web browser development, highlighting the critical need for regular security updates and the dangers of running outdated software in production environments.