CVE-2000-0310 in OpenBSD
Summary
by MITRE
IP fragment assembly in OpenBSD 2.4 allows a remote attacker to cause a denial of service by sending a large number of fragmented packets.
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Analysis
by VulDB Data Team • 05/29/2018
The vulnerability described in CVE-2000-0310 represents a critical flaw in the Internet Protocol fragment assembly mechanism within OpenBSD version 2.4. This issue resides in the kernel-level network stack implementation where the operating system fails to properly handle and reassemble fragmented IP packets. The vulnerability specifically targets the fragment reassembly process that occurs when multiple IP fragments arrive at the target system, with the kernel attempting to reconstruct the original datagram for processing. When an attacker sends a large number of fragmented packets designed to exploit this flaw, the system's fragment reassembly buffer becomes overwhelmed or corrupted, leading to system instability and potential denial of service conditions.
The technical root cause of this vulnerability stems from inadequate input validation and memory management during the IP fragment assembly process. The OpenBSD implementation lacks proper bounds checking and resource allocation controls when handling fragmented packets, particularly when dealing with overlapping or malformed fragments. This weakness allows attackers to craft packets that cause the kernel to allocate excessive memory resources or enter infinite loops during the reassembly process. The vulnerability falls under the category of resource exhaustion attacks as described in CWE-400, where the attacker consumes system resources in a manner that prevents legitimate operations from completing successfully. The flaw is particularly dangerous because IP fragmentation is a standard network operation that occurs frequently in various network environments, making the attack surface wide and difficult to predict or prevent.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can potentially lead to complete system crashes or reboot cycles in affected OpenBSD systems. Remote attackers can exploit this weakness without requiring any authentication or special privileges, making it a significant threat in networked environments where systems are exposed to untrusted network traffic. The vulnerability affects systems running OpenBSD 2.4 and potentially other versions that implement similar fragment reassembly logic, creating widespread exposure across networks that rely on this operating system. Attackers can leverage this flaw to disrupt network services, compromise system availability, and potentially create conditions that allow for more sophisticated attacks if the system becomes unstable or crashes. This vulnerability aligns with ATT&CK technique T1498 which focuses on network denial of service attacks, and T1566 which covers social engineering techniques that can be used to deliver such attacks.
Mitigation strategies for this vulnerability require immediate system updates to patched versions of OpenBSD that address the fragment reassembly logic. System administrators should ensure that all OpenBSD installations are updated to versions that contain proper bounds checking and resource management controls for IP fragment handling. Network administrators can implement packet filtering rules to limit the number of fragments that can be processed within a given timeframe or to drop suspicious fragmented traffic patterns. Additionally, monitoring network traffic for unusual fragment patterns can help detect potential exploitation attempts. The fix typically involves implementing proper memory allocation limits, adding timeout mechanisms for fragment reassembly, and ensuring that the kernel properly handles edge cases in fragment ordering and overlap detection. This vulnerability demonstrates the critical importance of proper resource management in kernel-level network code and highlights the need for comprehensive testing of network protocol implementations against malicious inputs.