CVE-1999-0001 in FreeBSD
Summary
by MITRE
ip_input.c in BSD-derived TCP/IP implementations allows remote attackers to cause a denial of service (crash or hang) via crafted packets.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-0001 represents a critical flaw in the network stack implementation of BSD-derived operating systems, specifically within the ip_input.c component that handles incoming IP packet processing. This issue demonstrates how fundamental network protocol implementations can contain logic errors that adversaries can exploit to disrupt system operations. The vulnerability exists in the core TCP/IP stack functionality that processes incoming packets, making it particularly dangerous as it affects the basic network communication capabilities of affected systems. The flaw was identified in the early 1990s and represents one of the earliest documented network stack vulnerabilities in the history of cybersecurity, highlighting the importance of robust input validation in network protocol implementations.
The technical root cause of this vulnerability lies in insufficient validation of incoming IP packet headers and their contents within the ip_input.c module. When malformed or specially crafted packets are received by a vulnerable system, the packet processing code fails to properly handle certain edge cases or invalid packet structures, leading to system crashes or indefinite hangs. This type of vulnerability falls under CWE-129, Input Validation, and specifically represents an improper input validation scenario where packet data is not adequately sanitized before processing. The flaw typically manifests when the system attempts to parse packet headers with unexpected values, particularly in fields such as packet length, version numbers, or header options that exceed normal bounds. The implementation lacks proper bounds checking and error handling mechanisms that would normally prevent such malformed data from causing system instability.
The operational impact of CVE-1999-0001 extends beyond simple system crashes to encompass broader network availability issues that can affect entire network services. When exploited, this vulnerability can cause individual hosts to become unresponsive, effectively creating a denial of service condition that impacts network connectivity and service availability. Attackers can leverage this vulnerability to target specific systems or entire networks, potentially causing cascading failures in network infrastructure. The vulnerability is particularly dangerous because it operates at the network protocol level, meaning that even systems with strong application-level security measures can be brought down through this attack vector. From an ATT&CK framework perspective, this vulnerability maps to T1498 - Network Denial of Service, and represents a classic example of how protocol-level flaws can be weaponized to create system-wide availability issues.
Mitigation strategies for this vulnerability require both immediate system-level patches and long-term architectural improvements in network protocol implementations. System administrators should prioritize applying the relevant security patches that were developed to address this specific issue in the affected BSD implementations. The patches typically involve adding proper bounds checking and input validation to the packet processing code, ensuring that malformed packets are either properly handled or rejected before they can cause system instability. Network administrators should also implement packet filtering rules at network boundaries to identify and drop suspicious traffic patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing intrusion detection systems that can monitor for patterns consistent with this vulnerability. The vulnerability underscores the importance of defensive programming practices and comprehensive testing of network protocol implementations, particularly in mission-critical systems where availability is paramount. Regular security assessments and code reviews of core network components can help identify similar vulnerabilities before they can be exploited by malicious actors.