CVE-2004-0171 in Mac OS X
Summary
by MITRE
FreeBSD 5.1 and earlier, and Mac OS X before 10.3.4, allows remote attackers to cause a denial of service (resource exhaustion of memory buffers and system crash) via a large number of out-of-sequence TCP packets, which prevents the operating system from creating new connections.
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Analysis
by VulDB Data Team • 12/15/2024
This vulnerability represents a classic resource exhaustion attack targeting the TCP connection handling mechanisms in operating systems. The flaw manifests when systems process a large volume of out-of-sequence TCP packets, causing the kernel to allocate memory buffers for each packet received. In FreeBSD versions 5.1 and earlier, as well as Mac OS X before 10.3.4, the TCP stack implementation lacks proper validation and rate limiting for packets arriving out of sequence, leading to unbounded memory allocation. The vulnerability operates at the network protocol level, specifically targeting the Transmission Control Protocol which governs reliable data transmission across networks. This type of attack falls under the category of denial of service attacks where the attacker consumes system resources to prevent legitimate operations from completing successfully.
The technical implementation of this vulnerability exploits the TCP state machine's handling of packet ordering and sequence numbers. When out-of-sequence packets arrive, the system maintains additional buffers and tracking structures to manage the reassembly process. In affected versions, the system does not implement adequate limits on the number of such packets that can be queued or buffered, allowing an attacker to send a continuous stream of out-of-order packets. Each packet triggers the allocation of memory structures to track the connection state, and as the number of these packets increases without proper cleanup or rate limiting, the system eventually exhausts its available memory resources. This memory exhaustion directly translates to system instability and complete service unavailability, as the kernel can no longer allocate the necessary resources to establish new connections or process legitimate traffic.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete system compromise and potential denial of service for all network services. Attackers can leverage this vulnerability to render entire systems unusable by consuming all available memory buffers and system resources. The attack requires minimal computational resources from the attacker side, making it particularly dangerous as it can be executed against systems with limited resources. Network administrators face significant challenges in detecting such attacks since they appear as legitimate network traffic patterns, and the system crash or resource exhaustion occurs gradually rather than instantaneously. The vulnerability affects core network functionality and can impact critical infrastructure services including web servers, database systems, and other network-dependent applications that rely on stable TCP connections.
Mitigation strategies for this vulnerability involve implementing proper rate limiting and packet validation mechanisms within the TCP stack. System administrators should apply vendor-specific patches and updates that address the memory allocation issues in the TCP implementation. The recommended approach includes configuring connection tracking limits, implementing TCP SYN cookies, and setting appropriate buffer limits for out-of-order packet handling. Network-level mitigations such as intrusion detection systems can help detect abnormal packet patterns that may indicate this attack. Additionally, implementing proper firewall rules to limit the rate of incoming packets and configuring operating system parameters to restrict memory allocation for TCP buffer management provides effective protection. Organizations should also consider implementing network segmentation and monitoring to detect unusual traffic patterns that could indicate exploitation attempts. This vulnerability highlights the importance of robust resource management in operating system kernels and the necessity of proper input validation for network protocols, aligning with common weakness enumerations such as CWE-131 and attack techniques documented in the mitre ATT&CK framework under network service disruption categories.