CVE-2004-0002 in FreeBSD
Summary
by MITRE
The TCP MSS (maximum segment size) functionality in netinet allows remote attackers to cause a denial of service (resource exhaustion) via (1) a low MTU, which causes a large number of small packets to be produced, or (2) via a large number of packets with a small TCP payload, which cause a large number of calls to the resource-intensive sowakeup function.
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Analysis
by VulDB Data Team • 06/18/2018
The vulnerability described in CVE-2004-0002 represents a significant denial of service weakness within the TCP implementation of network stacks, specifically affecting the handling of maximum segment size parameters. This flaw exists within the netinet subsystem where TCP MSS functionality is processed, creating conditions that can be exploited by remote attackers to exhaust system resources. The vulnerability manifests through two distinct attack vectors that leverage different aspects of TCP packet handling and network communication protocols. The first vector involves manipulating the Maximum Transmission Unit setting to force the generation of numerous small packets, while the second vector exploits the frequency of TCP payload processing through the sowakeup function.
The technical implementation of this vulnerability stems from how the TCP stack manages packet segmentation and resource allocation when processing network traffic. When an attacker manipulates the MTU parameter to a very low value, the TCP implementation must fragment larger data segments into numerous smaller packets to accommodate the limited transmission size. This fragmentation process, while normally handled efficiently, becomes problematic when executed at scale, leading to excessive memory allocation and processing overhead. The second attack vector specifically targets the sowakeup function, which is responsible for managing socket wake-up operations and resource notifications in the TCP stack. When attackers flood the system with numerous small TCP packets, they trigger repeated calls to this function, which is computationally expensive and consumes significant system resources. This function is designed to handle asynchronous events and notifications, but its repeated invocation under attack conditions leads to resource exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader system stability and performance degradation. Remote attackers can exploit these conditions to consume substantial memory resources, CPU cycles, and network bandwidth, effectively rendering affected systems unable to process legitimate network traffic. The resource exhaustion occurs at multiple levels within the network stack, affecting both kernel memory allocation and processing capacity. Systems running vulnerable implementations become increasingly susceptible to sustained attack scenarios where the cumulative effect of small packet processing gradually depletes available resources until complete service failure occurs. The vulnerability affects systems where the TCP stack does not properly implement rate limiting or resource management controls for packet processing, making it particularly dangerous in high-traffic network environments.
Mitigation strategies for this vulnerability should focus on implementing robust resource management controls and packet filtering mechanisms within network infrastructure. Network administrators should configure appropriate MTU values that prevent extreme fragmentation while maintaining efficient network utilization. The implementation of rate limiting controls for TCP packet processing can help prevent excessive calls to resource-intensive functions like sowakeup. System administrators should also consider implementing firewall rules that limit the number of small packets allowed through network boundaries and deploy intrusion detection systems that can identify patterns consistent with this attack methodology. According to CWE-400, this vulnerability relates to resource exhaustion issues that occur when systems fail to properly manage computational resources under attack conditions. The ATT&CK framework categorizes this as a resource exhaustion technique that targets system stability through manipulation of network protocol parameters. Organizations should also ensure that their network stacks are updated with patches that implement proper bounds checking and resource management for TCP MSS handling. Regular monitoring of system resource utilization and network traffic patterns can help identify potential exploitation attempts before they cause significant disruption to services.