CVE-1999-0222 in Cisco
Summary
by MITRE
Denial of service in Cisco IOS web server allows attackers to reboot the router using a long URL.
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Analysis
by VulDB Data Team • 04/18/2026
The vulnerability identified as CVE-1999-0222 represents a critical denial of service flaw within Cisco IOS web server implementations that affected numerous network devices from the late 1990s. This weakness specifically targeted the HTTP server functionality embedded within Cisco's Internet Operating System, which was commonly deployed on routers and switches to provide web-based management interfaces. The vulnerability emerged from inadequate input validation mechanisms within the web server component, creating a condition where malformed or excessively long URL parameters could trigger unexpected behavior in the underlying operating system.
The technical flaw manifests through a buffer overflow condition that occurs when the web server processes Uniform Resource Locators exceeding predetermined length thresholds. When an attacker crafts a specially constructed URL with an abnormally long string of characters, the IOS web server fails to properly validate the input length before processing the request. This lack of proper boundary checking causes the server to overwrite adjacent memory locations, ultimately leading to system instability and complete device reboot. The vulnerability operates at the application layer of the network stack and specifically affects the HTTP server daemon running within the IOS environment. The flaw demonstrates characteristics consistent with CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which addresses stack-based buffer overflow scenarios that can occur during string handling operations.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential network-wide consequences. When exploited, the denial of service condition can cause routers to become completely unresponsive, effectively severing network connectivity for all devices relying on that particular routing infrastructure. Network administrators managing multiple Cisco devices would face cascading failures if the vulnerability were exploited across several routers simultaneously, potentially resulting in widespread network outages. The attack vector is particularly concerning because it requires minimal technical expertise to execute, making it accessible to attackers with basic knowledge of web protocols and network infrastructure. The vulnerability's exploitation directly aligns with ATT&CK technique T1499.004, which describes network disruption attacks through denial of service mechanisms that target network infrastructure components.
Mitigation strategies for CVE-1999-0222 primarily focus on implementing immediate defensive measures while more comprehensive solutions are developed. Cisco released patches and firmware updates that addressed the buffer overflow condition by implementing proper input validation and length checking mechanisms within the web server component. Network administrators should prioritize applying these security updates to all affected devices and disable the web server functionality on routers when it is not actively required for management purposes. Additional protective measures include implementing network segmentation to isolate vulnerable devices, configuring access control lists to restrict web server access to trusted IP addresses, and deploying intrusion detection systems to monitor for suspicious URL patterns. The vulnerability highlights the importance of proper input validation and boundary checking in network infrastructure software, establishing a precedent for more rigorous security testing of embedded systems and web server implementations in telecommunications equipment. Organizations should maintain comprehensive inventory records of all network devices running vulnerable IOS versions and establish regular patch management protocols to prevent similar vulnerabilities from compromising network infrastructure.