CVE-2003-0364 in Linux
Summary
by MITRE
The TCP/IP fragment reassembly handling in the Linux kernel 2.4 allows remote attackers to cause a denial of service (CPU consumption) via certain packets that cause a large number of hash table collisions.
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Analysis
by VulDB Data Team • 06/25/2019
The vulnerability described in CVE-2003-0364 represents a critical flaw in the Linux kernel 2.4 TCP/IP stack implementation that specifically targets the fragment reassembly mechanism. This issue arises from the kernel's handling of IP fragments during the reassembly process, where maliciously crafted packets can exploit weaknesses in the hash table implementation used to track and manage fragmented data. The vulnerability operates at the network protocol level and affects systems running kernel versions prior to 2.4.21, making it particularly concerning given the widespread deployment of these older kernel versions in enterprise environments during that time period. The flaw demonstrates a classic example of a resource exhaustion attack that leverages protocol implementation weaknesses rather than direct exploitation of code execution vulnerabilities.
The technical root cause of this vulnerability lies in the hash table collision handling within the TCP/IP fragment reassembly code. When the Linux kernel receives fragmented IP packets, it uses a hash table to maintain references to incomplete fragments that need to be reassembled. The hash function used in the kernel's implementation was susceptible to collision attacks where an attacker could craft packets that would consistently map to the same hash bucket, causing the hash table to degenerate into a linked list structure. This degradation results in linear time complexity for hash table operations instead of the expected constant time performance, leading to massive CPU consumption as the kernel processes each fragment through increasingly longer collision chains. The vulnerability specifically targets the reassembly queue management where the kernel maintains a hash table of pending fragment reassembly operations, with each hash collision forcing the system to perform additional computational work to resolve the conflict.
The operational impact of CVE-2003-0364 manifests as a severe denial of service condition that can effectively render affected systems unusable. Attackers can trigger this vulnerability by sending a carefully constructed sequence of fragmented packets that force hash table collisions, causing the system's CPU utilization to spike to 100% or higher. The attack is particularly effective because it requires minimal computational resources from the attacker while generating maximum impact on the target system. Network services become unavailable as the kernel spends all its processing cycles managing the hash table collisions rather than processing legitimate network traffic. The vulnerability can be exploited against any system running vulnerable kernel versions, including web servers, database servers, and network infrastructure devices, making it a significant threat to network availability and system reliability. This type of attack aligns with the ATT&CK technique T1499.004 for network denial of service, specifically targeting system resources to prevent legitimate use.
The mitigation strategies for this vulnerability primarily involve kernel version upgrades to 2.4.21 or later, which contain patches that address the hash table collision handling issues in the fragment reassembly code. The kernel patches implemented in these versions typically involve improving the hash function to reduce collision probability or implementing more efficient collision resolution mechanisms. Organizations should also consider implementing network ingress filtering and rate limiting to reduce the impact of such attacks, though these measures only provide partial protection since the vulnerability can be triggered through legitimate network traffic patterns. The fix addresses the underlying CWE-327 weakness related to weak cryptographic hash functions and improper handling of hash table collisions, which are common issues in protocol implementations that can lead to resource exhaustion attacks. System administrators should prioritize patching this vulnerability as it represents a fundamental flaw in network stack implementation that can be exploited to cause complete system unavailability, making it a critical security concern for any organization relying on Linux systems for network services.