CVE-2024-20267: Cisco NX-OS MPLS Traffic DoS Vulnerability

CVE-2024-20267 Overview

A vulnerability exists in the handling of MPLS traffic for Cisco NX-OS Software that could allow an unauthenticated, remote attacker to cause the netstack process to unexpectedly restart. This could result in the affected device stopping network traffic processing or reloading entirely, leading to a denial of service (DoS) condition.

The vulnerability stems from improper error checking when processing ingress MPLS frames. An attacker can exploit this flaw by sending a specially crafted IPv6 packet encapsulated within an MPLS frame to an MPLS-enabled interface on the targeted device. Notably, the malicious IPv6 packet can be generated multiple hops away from the target and then encapsulated within MPLS, making attack attribution more difficult.

Critical Impact

Successful exploitation allows unauthenticated remote attackers to cause network infrastructure devices to stop processing traffic or reload, potentially disrupting critical network operations across enterprise environments.

Affected Products

• Cisco NX-OS versions 6.0(2) through 6.2(24a)
• Cisco NX-OS versions 7.0(3) through 7.3(0)
• Cisco NX-OS versions 9.2(1) through 10.4(1)

Discovery Timeline

• February 29, 2024 - CVE-2024-20267 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-20267

Vulnerability Analysis

This vulnerability affects the netstack process in Cisco NX-OS Software, which is responsible for handling network traffic on Cisco Nexus switches. The flaw occurs when the device processes MPLS-encapsulated IPv6 packets on interfaces where MPLS is enabled.

The vulnerability is classified as a buffer overflow (CWE-120), indicating that the improper error checking allows data to exceed allocated buffer boundaries during MPLS frame processing. When a malformed IPv6 packet arrives encapsulated within an MPLS frame, the netstack process fails to properly validate the frame contents, leading to process instability.

What makes this vulnerability particularly concerning is the ability for attackers to launch attacks from multiple network hops away. The malicious packet only needs to reach an MPLS-enabled interface on the target device, allowing attackers to potentially leverage MPLS infrastructure across service provider networks to reach their targets.

Root Cause

The root cause is a lack of proper error checking when processing ingress MPLS frames containing IPv6 packets. The netstack process does not adequately validate the structure and contents of MPLS-encapsulated traffic before processing, leading to a buffer overflow condition (CWE-120) that causes the process to crash.

When the netstack process encounters the malformed frame, it fails to handle the error gracefully, resulting in an unexpected restart. This can cascade into broader network disruption as the device may stop processing legitimate traffic or perform a full reload.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker exploits this vulnerability through the following sequence:

1. The attacker identifies a target Cisco NX-OS device with MPLS-enabled interfaces
2. A specially crafted IPv6 packet is constructed with malformed data designed to trigger the buffer overflow
3. The IPv6 packet is encapsulated within an MPLS frame
4. The MPLS frame is sent toward the target device, potentially traversing multiple network hops
5. When the target device processes the malformed MPLS frame on an MPLS-enabled interface, the netstack process crashes
6. The device either stops processing network traffic or performs a full reload

The attack can be sustained to create a persistent denial of service condition by repeatedly sending malicious packets.

Detection Methods for CVE-2024-20267

Indicators of Compromise

• Unexpected restarts of the netstack process on Cisco NX-OS devices
• Device reloads without administrative action or apparent cause
• Network traffic processing interruptions on MPLS-enabled interfaces
• Syslog messages indicating netstack process crashes or core dumps

Detection Strategies

• Monitor for repeated netstack process restarts using show process commands and logging
• Implement network traffic analysis to detect anomalous MPLS-encapsulated IPv6 traffic patterns
• Configure SNMP traps to alert on unexpected device reloads or process crashes
• Review system logs for core dump generation events related to the netstack process

Monitoring Recommendations

• Enable detailed logging on MPLS-enabled interfaces to capture traffic anomalies
• Deploy network monitoring solutions to track device availability and process health
• Configure alerting thresholds for process restart frequency on critical network infrastructure
• Implement baseline monitoring to detect deviations in MPLS traffic patterns

How to Mitigate CVE-2024-20267

Immediate Actions Required

• Review the Cisco Security Advisory to determine if your NX-OS version is affected
• Inventory all Cisco NX-OS devices with MPLS-enabled interfaces in your environment
• Plan and schedule patching for affected devices during maintenance windows
• Monitor affected devices for signs of exploitation while awaiting patch deployment

Patch Information

Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory to identify the appropriate fixed software release for their specific NX-OS version and platform.

The advisory provides detailed information about affected versions and the corresponding fixed releases across the following version trains:

• NX-OS 6.x series
• NX-OS 7.x series
• NX-OS 9.x series
• NX-OS 10.x series

Organizations should prioritize patching based on the criticality of affected devices and their exposure to potentially malicious MPLS traffic.

Workarounds

• If MPLS functionality is not required, consider disabling MPLS on affected interfaces to eliminate the attack surface
• Implement access control lists (ACLs) to restrict which sources can send MPLS traffic to affected devices
• Deploy network segmentation to limit exposure of MPLS-enabled interfaces to trusted network segments only
• Consider implementing rate limiting on MPLS traffic to reduce the impact of potential exploitation attempts

# Example: Check MPLS configuration status on NX-OS
show running-config | include mpls
show mpls switching
show mpls interfaces

# Example: Verify current NX-OS version
show version

# Example: Check netstack process status
show processes | include netstack