CVE-2024-20480 Overview
A vulnerability exists in the DHCP Snooping feature of Cisco IOS XE Software on Software-Defined Access (SD-Access) fabric edge nodes that could allow an unauthenticated, remote attacker to cause high CPU utilization on an affected device, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of IPv4 DHCP packets, where specifically crafted DHCP packets can cause the device to exhaust CPU resources and stop processing traffic. The DoS condition requires a manual reload to recover, making this a particularly disruptive attack vector for enterprise networks relying on SD-Access fabric deployments.
Critical Impact
Unauthenticated remote attackers can cause complete network device unavailability requiring manual intervention to restore service, potentially affecting entire SD-Access fabric segments.
Affected Products
- Cisco IOS XE versions 16.1.1 through 16.12.11
- Cisco IOS XE versions 17.1.1 through 17.14.1a
- Cisco Software-Defined Access (SD-Access) fabric edge nodes with DHCP Snooping enabled
Discovery Timeline
- September 25, 2024 - CVE-2024-20480 published to NVD
- October 3, 2024 - Last updated in NVD database
Technical Details for CVE-2024-20480
Vulnerability Analysis
This denial of service vulnerability affects the DHCP Snooping feature within Cisco IOS XE Software specifically deployed on SD-Access fabric edge nodes. The vulnerability stems from improper handling of IPv4 DHCP packets, leading to a resource exhaustion condition. When exploited, the affected device experiences high CPU utilization that prevents it from processing legitimate network traffic.
The attack can be executed remotely without authentication, meaning any attacker with network access to the affected device can trigger the condition. The scope of the vulnerability extends beyond the vulnerable component itself, as the DoS condition can impact network connectivity for all devices relying on the affected edge node. Critically, the device cannot recover automatically and requires a manual reload to restore normal operation, significantly increasing the operational impact.
Root Cause
The vulnerability is attributed to two related weaknesses: improper handling of operator expressions in expected-behavior checks (CWE-783) and insecure state management within the DHCP Snooping feature (CWE-670). The DHCP Snooping process fails to properly validate and handle certain malformed or specially crafted IPv4 DHCP packets, allowing an attacker to trigger a condition where the processing logic consumes excessive CPU resources without proper resource limits or timeout mechanisms.
Attack Vector
An attacker exploits this vulnerability by sending specially crafted IPv4 DHCP packets to an affected Cisco IOS XE device configured as an SD-Access fabric edge node with DHCP Snooping enabled. The attack requires network access to reach the target device but does not require any authentication or user interaction.
The attack flow involves:
- Identifying a target device running a vulnerable version of Cisco IOS XE configured as an SD-Access fabric edge node
- Crafting malicious IPv4 DHCP packets designed to trigger improper packet handling
- Sending the crafted packets to the target device
- The device's DHCP Snooping feature processes these packets incorrectly, leading to CPU resource exhaustion
- The device stops processing traffic, causing a denial of service condition
- Recovery requires a manual reload of the affected device
Detection Methods for CVE-2024-20480
Indicators of Compromise
- Sudden and sustained high CPU utilization on SD-Access fabric edge nodes running Cisco IOS XE
- Device becomes unresponsive to management commands and stops forwarding traffic
- Increased volume of DHCP traffic from unusual sources targeting the affected device
- Network outages affecting endpoints connected through the compromised fabric edge node
Detection Strategies
- Monitor CPU utilization metrics on all Cisco IOS XE devices configured as SD-Access fabric edge nodes for abnormal spikes
- Implement network traffic analysis to detect unusual patterns or volumes of DHCP traffic targeting edge nodes
- Configure SNMP traps and syslog alerts for high CPU utilization events on network devices
- Deploy network behavior anomaly detection to identify potential exploitation attempts
Monitoring Recommendations
- Establish baseline CPU utilization metrics for SD-Access fabric edge nodes and alert on deviations
- Implement continuous monitoring of DHCP-related processes and packet rates on vulnerable devices
- Use network management systems to track device availability and response times across the SD-Access fabric
- Review device logs regularly for signs of abnormal DHCP packet processing or resource exhaustion
How to Mitigate CVE-2024-20480
Immediate Actions Required
- Identify all Cisco IOS XE devices deployed as SD-Access fabric edge nodes with DHCP Snooping enabled
- Review the Cisco Security Advisory to determine the fixed software versions applicable to your deployment
- Plan and schedule upgrades to patched versions of Cisco IOS XE as recommended by Cisco
- Consider network segmentation to limit exposure of vulnerable devices while awaiting patches
Patch Information
Cisco has released security updates to address this vulnerability. Organizations should consult the official Cisco Security Advisory for CVE-2024-20480 to identify the specific fixed release versions for their deployed IOS XE version trains. The advisory includes a comprehensive table mapping vulnerable versions to their corresponding fixed releases across all affected version branches from 16.1.x through 17.14.x.
Workarounds
- Evaluate whether DHCP Snooping is a required feature for your environment; if not essential, consider disabling it temporarily
- Implement access control lists (ACLs) to restrict DHCP traffic to only authorized DHCP servers and relay agents
- Deploy rate limiting for DHCP traffic on interfaces where possible to reduce the impact of potential exploitation
- Segment network architecture to isolate SD-Access fabric edge nodes from untrusted network segments
# Example: Configure ACL to restrict DHCP traffic to authorized servers
# Consult Cisco documentation for your specific deployment
configure terminal
ip access-list extended DHCP-RESTRICT
permit udp host <AUTHORIZED_DHCP_SERVER> eq 67 any eq 68
permit udp any eq 68 host <AUTHORIZED_DHCP_SERVER> eq 67
deny udp any any eq 67
deny udp any any eq 68
permit ip any any
exit
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
