CVE-2019-1750 in IOS XE
Summary
by MITRE
A vulnerability in the Easy Virtual Switching System (VSS) of Cisco IOS XE Software on Catalyst 4500 Series Switches could allow an unauthenticated, adjacent attacker to cause the switches to reload. The vulnerability is due to incomplete error handling when processing Cisco Discovery Protocol (CDP) packets used with the Easy Virtual Switching System. An attacker could exploit this vulnerability by sending a specially crafted CDP packet. An exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 08/17/2023
The vulnerability identified as CVE-2019-1750 represents a critical denial of service weakness within Cisco IOS XE Software operating on Catalyst 4500 Series Switches. This flaw specifically affects the Easy Virtual Switching System implementation, which is designed to provide seamless network redundancy and virtual switching capabilities. The vulnerability stems from inadequate error handling mechanisms within the software's processing of Cisco Discovery Protocol packets, a standard network protocol used for device discovery and network topology mapping. The affected switches operate under the assumption that CDP packets will conform to expected formats, but fail to properly validate or sanitize incoming packets before processing them within the VSS framework.
The technical exploitation of this vulnerability requires an attacker to be physically adjacent to the target switch, as the flaw does not permit remote exploitation across network boundaries. This adjacency requirement aligns with attack pattern classification under the MITRE ATT&CK framework, specifically relating to the 'Network Service Scan' and 'Exploitation for Client Execution' techniques. The attacker must craft a malicious CDP packet that triggers the incomplete error handling condition within the VSS processing module. When the switch receives and attempts to process this malformed packet, the system fails to properly manage the error state, leading to a complete system reload or crash. This behavior manifests as an immediate denial of service condition, effectively rendering the switch non-operational until manual intervention or automatic recovery occurs.
The operational impact of this vulnerability extends beyond simple service disruption, as the Catalyst 4500 Series switches often serve as core network infrastructure components within enterprise and service provider environments. When these switches experience reloads, they can cause cascading failures throughout connected networks, particularly in virtual switching environments where multiple physical devices are logically grouped into single virtual entities. The DoS condition affects not only the immediate switch but can also impact network redundancy systems that depend on VSS functionality, potentially leading to broader network outages. The vulnerability's presence in widely deployed Catalyst 4500 series hardware means that organizations may face significant operational disruption, as these switches are commonly found in data center core networks and service provider access networks where uptime is critical.
Organizations should implement immediate mitigations including network segmentation to limit physical access to affected switches, deployment of access control lists to filter CDP traffic, and monitoring for anomalous CDP packet patterns. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception," and represents a classic example of improper exception handling in network protocol processing. Cisco has released software updates addressing this vulnerability through IOS XE patches that enhance CDP packet validation and improve error handling within the VSS subsystem. Network administrators should also consider implementing network intrusion detection systems capable of identifying and blocking malicious CDP packets, as well as establishing robust monitoring procedures to detect switch reload events that could indicate exploitation attempts. The remediation process requires careful planning to minimize network disruption during patch deployment, particularly in environments where VSS configurations are critical to network operations.