CVE-2001-1554 in AIX
Summary
by MITRE
IBM AIX 430 does not properly unlock IPPMTU_LOCK, which allows remote attackers to cause a denial of service (hang) via Path Maximum Transmit Unit (PMTU) IP packets.
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Analysis
by VulDB Data Team • 01/14/2018
The vulnerability described in CVE-2001-1554 represents a critical flaw in IBM AIX 430 operating system implementation that affects the Internet Protocol (IP) packet processing mechanisms. This issue specifically targets the IPPMTU_LOCK mechanism which is responsible for managing Path Maximum Transmit Unit (PMTU) discovery operations within the network stack. The improper handling of this lock mechanism creates a condition where remote attackers can exploit the system's response to PMTU packets to trigger a denial of service scenario. The vulnerability exists at the kernel level within the IP networking subsystem, making it particularly dangerous as it can be leveraged by attackers without requiring local system access or authentication credentials. This type of vulnerability falls under the category of resource exhaustion or lock contention issues that can lead to system instability and complete service disruption.
The technical flaw manifests when the system receives specially crafted PMTU packets that cause the IPPMTU_LOCK to remain in an unlocked state or become improperly managed during the processing of these packets. This condition prevents the system from properly handling subsequent IP traffic and can lead to the system becoming unresponsive or hanging. The vulnerability specifically affects the IP packet processing logic where the system fails to correctly release or manage the lock associated with PMTU discovery operations. When multiple PMTU packets are sent in rapid succession or in a manner designed to exploit the lock mechanism, the system becomes unable to process additional network traffic properly, effectively creating a denial of service condition that can persist until the system is manually restarted or the lock is eventually released through normal system operation. This behavior aligns with CWE-664, which describes improper control of a resource through lifetime management issues, and specifically relates to improper locking mechanisms that can lead to resource exhaustion or system hang conditions.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of critical network services running on affected IBM AIX systems. Organizations relying on these systems for mission-critical applications face significant risk of service interruption when attackers exploit this vulnerability, particularly in environments where network availability is paramount. The remote nature of the attack means that systems can be compromised from anywhere on the network, making it difficult to contain or prevent the exploitation. Network administrators must be aware that this vulnerability can affect not just individual hosts but potentially entire network segments if multiple systems are running the vulnerable IBM AIX version. The attack vector through PMTU packets is particularly insidious because these are legitimate network operations that occur during normal IP communication, making them difficult to detect or filter without significant network monitoring and anomaly detection capabilities.
Mitigation strategies for this vulnerability should focus on immediate patch application from IBM, which would address the improper lock management in the IPPMTU_LOCK mechanism. Organizations should also implement network monitoring solutions capable of detecting abnormal PMTU packet patterns that could indicate exploitation attempts. Network segmentation and access controls should be enforced to limit exposure of vulnerable systems to untrusted networks. Additionally, implementing rate limiting on PMTU-related packets and configuring firewalls to filter suspicious traffic patterns can provide additional defense in depth. The vulnerability demonstrates the importance of proper synchronization mechanisms in kernel-level code and highlights the need for comprehensive testing of locking protocols in operating system implementations. System administrators should also consider implementing intrusion detection systems specifically designed to monitor for network-level denial of service attacks and maintain detailed logs of network traffic patterns for forensic analysis in case of successful exploitation attempts. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date system patches and the potential consequences of running unsupported or unpatched operating system versions.