CVE-2020-3221 in IOS XE
Summary
by MITRE
A vulnerability in the Flexible NetFlow Version 9 packet processor of Cisco IOS XE Software for Cisco Catalyst 9800 Series Wireless Controllers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper validation of parameters in a Flexible NetFlow Version 9 record. An attacker could exploit this vulnerability by sending a malformed Flexible NetFlow Version 9 packet to the Control and Provisioning of Wireless Access Points (CAPWAP) data port of an affected device. An exploit could allow the attacker to trigger an infinite loop, resulting in a process crash that would cause a reload of the device.
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Analysis
by VulDB Data Team • 10/21/2020
The vulnerability identified as CVE-2020-3221 resides within the Flexible NetFlow Version 9 packet processor of Cisco IOS XE Software operating on Cisco Catalyst 9800 Series Wireless Controllers. This critical weakness represents a failure in input validation mechanisms that specifically targets the processing of NetFlow records within the network infrastructure. The affected device operates as a wireless access controller that manages wireless network access points through the CAPWAP protocol, making it a prime target for network-level attacks that can disrupt wireless connectivity across enterprise environments.
The technical flaw manifests through inadequate parameter validation within the Flexible NetFlow Version 9 record processing logic. When an attacker crafts and transmits a malformed NetFlow Version 9 packet to the CAPWAP data port, the system fails to properly sanitize the incoming data before processing. This insufficient validation creates a condition where specific parameter combinations can trigger an infinite loop within the processing routine, causing the targeted process to consume excessive CPU resources without proper termination conditions. The vulnerability operates at the network protocol level, specifically within the flow monitoring and reporting mechanisms that are integral to network management and security operations.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire wireless infrastructure managed by the affected controller. When the infinite loop is triggered, it results in a complete process crash that cascades into a system reload, effectively taking the wireless controller offline for an extended period. This disruption directly affects wireless network availability and can impact business operations, particularly in environments where wireless connectivity is critical for operations. The DoS condition affects not only the immediate device but also the wireless access points under its management, potentially creating widespread network outages that can last from several minutes to hours depending on the recovery process.
Mitigation strategies for CVE-2020-3221 should focus on both immediate protective measures and long-term architectural improvements. Network administrators should implement access control lists and firewall rules to restrict access to the CAPWAP data port from untrusted networks, effectively limiting the attack surface. Cisco recommends applying the latest software patches and updates that contain fixes for the parameter validation issues within the NetFlow processor. Additionally, implementing network monitoring solutions that can detect anomalous NetFlow packet patterns and automatically alert administrators to potential exploitation attempts provides an additional layer of defense. The vulnerability aligns with CWE-129, which describes improper validation of input ranges, and represents a typical example of how insufficient input validation can lead to denial of service conditions. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network disruption through denial of service attacks, and demonstrates how attackers can leverage protocol implementation flaws to achieve system compromise.
Organizations should also consider implementing network segmentation strategies that isolate wireless controllers from general network traffic, reducing the potential attack vectors available to malicious actors. Regular security assessments and vulnerability scanning should include verification of the patched status of all wireless controllers to ensure complete protection. The incident highlights the importance of proper input validation in network protocol implementations and underscores the critical need for robust error handling mechanisms in infrastructure devices that process external network traffic. Continuous monitoring of system logs for process crash patterns and unusual CPU utilization spikes can help detect exploitation attempts before they result in complete service disruption.