CVE-2025-20162: Denial of Service Vulnerability in Cisco IOS XE Software

Overview

The cybersecurity sphere has been rocked by the discovery of a new and potentially devastating vulnerability, CVE-2025-20162, that affects the DHCP snooping security feature of Cisco IOS XE Software. This vulnerability is noteworthy due to its ability to cause a full interface queue wedge, leading to a potential denial of service (DoS) condition. It is of utmost concern to network administrators and system operators who rely on Cisco IOS XE Software for their networking needs.
The vulnerability matters because it enables an unauthenticated, remote attacker to potentially disrupt and compromise system operations, leading to significant downtime and potential data leakage. Given Cisco’s widespread use in the enterprise, this vulnerability may have far-reaching implications for businesses, institutions, and even governments worldwide.

Vulnerability Summary

CVE ID: CVE-2025-20162
Severity: High – 8.6 (CVSS score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Denial of Service and potential system compromise or data leakage

Affected Products

Product | Affected Versions

Cisco IOS XE Software | All versions before the patch

How the Exploit Works

This vulnerability stems from improper handling of DHCP request packets by Cisco IOS XE Software. An attacker can exploit this vulnerability by sending malicious DHCP request packets to the affected device. These packets, once received, can cause a full interface queue wedge, leading to a denial of service condition for downstream devices.
This vulnerability can be exploited with either unicast or broadcast DHCP packets on a VLAN that does not have DHCP snooping enabled, making it more challenging to detect and mitigate.

Conceptual Example Code

Below is a conceptual example of how an attacker might send malicious DHCP request packets:

#!/bin/bash
# A conceptual bash script to send DHCP request packets
for i in {1..1000}
do
echo "Sending DHCP request packet number $i"
echo -e "\x01\x01\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" | nc -u -w1 [target IP] 67
done

Please note that this code is for illustrative purposes only and is neither functional nor recommended for testing without proper authorization and precautions.

Recommended Mitigation

The recommended mitigation strategy for this vulnerability is to apply the vendor patch, which Cisco has released in response to the vulnerability. In situations where immediate patching is not possible, deploying a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can serve as a temporary mitigation measure to detect and block malicious DHCP request packets.