CVE-1999-0909 in Windows
Summary
by MITRE
Multihomed Windows systems allow a remote attacker to bypass IP source routing restrictions via a malformed packet with IP options, aka the "Spoofed Route Pointer" vulnerability.
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Analysis
by VulDB Data Team • 04/19/2026
The CVE-1999-0909 vulnerability represents a critical security flaw in multihomed windows systems that enables remote attackers to circumvent IP source routing restrictions through the manipulation of malformed packets containing IP options. This vulnerability specifically targets systems configured with multiple network interfaces or IP addresses, creating a complex attack surface where malicious actors can exploit the inherent weaknesses in how these systems process routing information. The flaw operates at the network protocol level, fundamentally undermining the security mechanisms designed to prevent unauthorized route manipulation and source address spoofing. The vulnerability's impact is particularly severe in environments where network segmentation and access control are paramount, as it allows attackers to potentially bypass firewalls and other network security controls that rely on proper source routing validation.
The technical implementation of this vulnerability stems from how Windows systems handle IP options within packets, specifically when processing route pointer information embedded in IP headers. When a system receives a packet with malformed IP options that contain spoofed route pointers, the operating system's network stack fails to properly validate the source routing information, allowing the attacker to inject packets that appear to originate from trusted network segments. This behavior violates fundamental principles of network security where systems should validate that packets are routed through legitimate paths before accepting them as legitimate traffic. The vulnerability is classified under CWE-264 as a privilege escalation through improper access control, specifically involving the manipulation of network routing information. According to ATT&CK framework, this vulnerability maps to T1071.004 for application layer protocol and T1566 for credential access through social engineering, as attackers can leverage this flaw to establish unauthorized network access and potentially escalate privileges.
The operational impact of CVE-1999-0909 extends far beyond simple network disruption, as it provides attackers with a pathway to bypass network security controls and potentially gain unauthorized access to sensitive systems. In multihomed environments where a single system connects to multiple networks or segments, this vulnerability allows attackers to craft packets that appear to originate from internal trusted networks, effectively enabling them to perform network reconnaissance and lateral movement attacks. The vulnerability is particularly dangerous because it operates at the network layer, making detection more challenging and allowing attackers to remain undetected while performing malicious activities. Organizations using Windows systems in complex network environments face significant risk, as this vulnerability can be exploited to gain unauthorized access to systems that would otherwise be protected by network segmentation. The attack vector typically involves sending specially crafted packets with malformed IP options that contain spoofed route information, causing the target system to accept packets as legitimate traffic from trusted sources.
Mitigation strategies for CVE-1999-0909 require a multi-layered approach that addresses both immediate system-level fixes and broader network security controls. The most effective immediate solution involves implementing proper IP source routing restrictions on affected Windows systems, disabling the processing of IP options that could contain spoofed route pointers, and configuring network security devices to drop packets with malformed IP options. Network administrators should implement ingress and egress filtering policies that validate source addresses against expected routing paths and establish proper access controls to prevent unauthorized packet injection. According to industry best practices and NIST guidelines, organizations should disable IP source routing entirely on systems that do not require it, as this eliminates the attack surface entirely. Additionally, implementing network intrusion detection systems that can identify and alert on malformed IP packets containing suspicious route pointer information provides an additional layer of defense. Regular security assessments and network audits should verify that systems properly implement source routing restrictions and that network configurations do not inadvertently enable this vulnerability. The vulnerability also highlights the importance of keeping network security controls updated and maintaining comprehensive network monitoring to detect anomalous routing behavior that could indicate exploitation attempts.