CVE-2001-0428 in VPN 3000 Concentrator
Summary
by MITRE
Cisco VPN 3000 series concentrators before 2.5.2(F) allow remote attackers to cause a denial of service via an IP packet with an invalid IP option.
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Analysis
by VulDB Data Team • 06/17/2019
The Cisco VPN 3000 series concentrators represent critical network infrastructure devices that facilitate secure remote access and site-to-site connections for enterprise networks. These appliances serve as gateways between remote users and corporate networks, making them prime targets for adversaries seeking to disrupt business operations. The vulnerability described in CVE-2001-0428 specifically affects versions prior to 2.5.2(F) and demonstrates a fundamental flaw in the processing of Internet Protocol packets. This weakness allows remote attackers to exploit the device's handling of malformed IP options, potentially leading to complete service disruption. The vulnerability exists within the network protocol stack implementation where the concentrator fails to properly validate incoming IP packet structures before processing them for routing or security purposes.
The technical flaw manifests when the Cisco VPN 3000 concentrator receives an IP packet containing invalid IP options. IP options are optional fields that can be included in IP packets to provide additional functionality such as source routing or record route capabilities. When these options contain malformed data or violate established IP protocol specifications, the concentrator's packet processing routine does not adequately validate the option structure. This validation failure causes the device to enter an unstable state where it either crashes completely or becomes unresponsive to legitimate traffic. The vulnerability specifically targets the IP packet processing module which is responsible for examining incoming packets before they are forwarded or subjected to security policies. The flaw represents a classic buffer overflow or input validation issue that has been categorized under CWE-129 as an insufficient validation of input boundaries, though the exact nature of the vulnerability may involve improper handling of option length fields within the IP header.
The operational impact of this vulnerability extends beyond simple service disruption to encompass significant business continuity risks for organizations relying on these concentrators for remote access capabilities. When exploited, the denial of service condition renders the entire VPN concentrator unavailable, effectively cutting off remote access for all users and potentially disrupting critical business processes. Network administrators may experience extended downtime while troubleshooting the issue, as the device typically requires a complete reboot to recover from the malformed packet attack. The remote nature of the exploit means that attackers can initiate the attack from anywhere on the internet without requiring physical access or authentication credentials, making it particularly dangerous for organizations with limited network monitoring capabilities. This vulnerability directly impacts the availability component of the CIA triad and can be categorized under the ATT&CK technique T1498 for network denial of service attacks, where adversaries target network infrastructure to disrupt operations.
Mitigation strategies for this vulnerability should prioritize immediate software updates to version 2.5.2(F) or later, as provided by Cisco's security advisory. Organizations should also implement network segmentation and access control measures to limit exposure of the affected concentrators to untrusted networks. Network monitoring solutions should be configured to detect anomalous packet patterns that may indicate exploitation attempts, particularly focusing on unusual IP option structures. The implementation of ingress filtering and egress filtering policies can help prevent malformed packets from reaching the concentrator in the first place. Additionally, organizations should conduct regular vulnerability assessments to identify other potentially affected devices and ensure that all network infrastructure components receive timely security updates. The vulnerability highlights the importance of robust input validation in network protocol implementations and serves as a reminder of the critical need for maintaining up-to-date security patches in network infrastructure devices. Organizations should also consider implementing redundant VPN concentrator configurations to provide failover capabilities in case of successful exploitation attempts.