CVE-2024-20446 Overview
A vulnerability in the DHCPv6 relay agent of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper handling of specific fields in a DHCPv6 RELAY-REPLY message. An attacker could exploit this vulnerability by sending a crafted DHCPv6 packet to any IPv6 address that is configured on an affected device. A successful exploit could allow the attacker to cause the dhcp_snoop process to crash and restart multiple times, causing the affected device to reload and resulting in a DoS condition.
Critical Impact
Unauthenticated remote attackers can crash network infrastructure devices through malformed DHCPv6 packets, causing service outages across the enterprise network.
Affected Products
- Cisco NX-OS Software with DHCPv6 relay agent enabled
- Cisco Nexus switches running vulnerable NX-OS versions
- Network devices with IPv6 addresses configured and DHCPv6 relay functionality active
Discovery Timeline
- 2024-08-28 - CVE-2024-20446 published to NVD
- 2024-08-29 - Last updated in NVD database
Technical Details for CVE-2024-20446
Vulnerability Analysis
This vulnerability is classified as a Null Pointer Dereference (CWE-476), a type of memory corruption issue that occurs when the software dereferences a pointer that it expects to be valid but is actually null. In this case, the dhcp_snoop process in Cisco NX-OS fails to properly validate specific fields within DHCPv6 RELAY-REPLY messages before processing them.
The vulnerability can be triggered remotely without authentication, meaning any attacker with network access to an IPv6-enabled interface on the affected device can potentially exploit it. The attack does not require user interaction and can be executed across network boundaries, making it particularly dangerous for internet-facing or multi-tenant network infrastructure.
A successful exploitation results in the dhcp_snoop process crashing and attempting to restart. If the attack is sustained or repeated, the process may crash multiple times in succession, triggering a device reload as a protective measure. This results in complete loss of network services provided by the affected device until it fully recovers.
Root Cause
The root cause of CVE-2024-20446 is improper handling of specific fields within DHCPv6 RELAY-REPLY messages. When the DHCPv6 relay agent receives a specially crafted packet, it fails to perform adequate validation on certain message fields before dereferencing associated pointers. This leads to a null pointer dereference condition when unexpected or malformed data is encountered, causing the dhcp_snoop process to crash.
The vulnerability stems from insufficient input validation in the DHCPv6 message parsing logic, where the code assumes fields will contain valid data without performing proper boundary and null checks.
Attack Vector
The attack is network-based and can be executed by an unauthenticated remote attacker. The attacker needs to craft a malicious DHCPv6 packet with specific malformed fields in the RELAY-REPLY message structure. This packet must be sent to any IPv6 address configured on the affected device.
The attack scenario involves:
- The attacker identifies a target Cisco NX-OS device with DHCPv6 relay agent functionality enabled
- The attacker crafts a DHCPv6 RELAY-REPLY message with malformed fields designed to trigger the null pointer dereference
- The packet is transmitted to any IPv6 address on the target device
- The dhcp_snoop process encounters the malformed fields and crashes
- Repeated exploitation causes multiple crashes, eventually triggering a device reload
For technical details on the vulnerability mechanism and packet structure, refer to the Cisco Security Advisory.
Detection Methods for CVE-2024-20446
Indicators of Compromise
- Repeated crashes of the dhcp_snoop process in system logs
- Unexpected device reloads with crash reasons pointing to DHCPv6 processing
- Abnormal volumes of DHCPv6 traffic targeting device management or infrastructure IPv6 addresses
- Core dumps indicating null pointer dereference in DHCPv6 relay agent code paths
Detection Strategies
- Monitor NX-OS system logs for dhcp_snoop process crash events and restart patterns
- Implement network-based intrusion detection rules to identify malformed DHCPv6 RELAY-REPLY packets
- Configure SNMP traps for process crashes and unexpected device reloads
- Deploy flow analysis to detect unusual DHCPv6 traffic patterns targeting infrastructure devices
Monitoring Recommendations
- Enable enhanced logging for DHCPv6 relay agent operations on NX-OS devices
- Configure syslog forwarding to a centralized SIEM for correlation and alerting
- Establish baseline metrics for DHCPv6 traffic and alert on anomalies
- Implement automated health checks that verify dhcp_snoop process status
How to Mitigate CVE-2024-20446
Immediate Actions Required
- Review the Cisco Security Advisory for affected versions and available patches
- Identify all Cisco NX-OS devices in your environment running DHCPv6 relay agent functionality
- Prioritize patching for internet-facing and critical infrastructure devices
- Consider temporarily disabling DHCPv6 relay agent on non-essential devices until patching is complete
Patch Information
Cisco has released software updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed software versions and upgrade instructions. The advisory provides detailed information about affected releases and the appropriate upgrade paths for different NX-OS platforms.
Workarounds
- Disable DHCPv6 relay agent functionality if not required in your environment
- Implement IPv6 access control lists (ACLs) to restrict DHCPv6 traffic to trusted sources only
- Deploy network segmentation to limit exposure of NX-OS management and infrastructure interfaces
- Use Control Plane Policing (CoPP) to rate-limit DHCPv6 traffic to the device
# Example: Disable DHCPv6 relay agent on NX-OS
configure terminal
no ipv6 dhcp relay
exit
copy running-config startup-config
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
