CVE-2003-0244 in Linux
Summary
by MITRE
The route cache implementation in Linux 2.4, and the Netfilter IP conntrack module, allows remote attackers to cause a denial of service (CPU consumption) via packets with forged source addresses that cause a large number of hash table collisions.
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Analysis
by VulDB Data Team • 03/08/2021
The vulnerability described in CVE-2003-0244 represents a critical flaw in the Linux kernel's network stack implementation that specifically affects versions 2.4 and earlier. This issue resides within the route cache mechanism and the Netfilter IP conntrack module, which are fundamental components responsible for managing network connections and routing decisions in Linux systems. The vulnerability stems from the way these modules handle packet processing when confronted with forged source addresses, creating a scenario where malicious actors can exploit the underlying hash table implementation to consume excessive CPU resources.
The technical flaw manifests when remote attackers craft packets with deliberately forged source IP addresses that are designed to collide within the hash tables used by the route cache and connection tracking systems. This collision behavior occurs because both components utilize hash tables for efficient lookup of routing information and connection states, but the hash functions employed are susceptible to adversarial inputs. When attackers send packets with carefully constructed source addresses, they can force multiple entries to map to the same hash bucket, creating a pathological case where the hash table performance degrades significantly from O(1) to O(n) complexity. This degradation results in the kernel spending excessive CPU cycles processing these hash collisions rather than handling legitimate network traffic.
The operational impact of this vulnerability is severe and directly translates to a denial of service condition that can render affected systems unusable. Systems exposed to this attack will experience dramatic increases in CPU utilization as the kernel struggles to process the artificially created hash collisions. The resource exhaustion occurs at the kernel level, making it particularly challenging to mitigate since traditional network-level defenses may not be effective against this type of attack. Network administrators may observe system sluggishness, unresponsiveness, or complete service interruption as the kernel becomes overwhelmed with processing hash table collisions. The vulnerability affects systems that rely heavily on network connectivity and connection tracking, making it particularly dangerous for servers, routers, and firewalls that process large volumes of network traffic.
Mitigation strategies for this vulnerability involve both immediate defensive measures and long-term architectural improvements. The most effective immediate solution is to upgrade to Linux kernel versions 2.6 and later, where the hash table implementations have been significantly improved to handle adversarial inputs more gracefully. System administrators should also implement rate limiting and connection tracking restrictions that limit the number of entries that can be created within a given time period. Additionally, implementing proper ingress and egress filtering can help reduce the effectiveness of this attack by preventing packets with forged source addresses from entering the network. The vulnerability aligns with CWE-124, which addresses weakness in the implementation of hash table collision handling, and relates to ATT&CK technique T1499.004 for resource exhaustion attacks. Organizations should also consider implementing network monitoring solutions that can detect unusual CPU utilization patterns and hash table behavior to provide early warning of potential exploitation attempts.