CVE-2020-3566: Cisco IOS XR DVMRP DOS Vulnerability

CVE-2020-3566 Overview

A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to exhaust process memory of an affected device. The vulnerability is due to insufficient queue management for Internet Group Management Protocol (IGMP) packets. An attacker could exploit this vulnerability by sending crafted IGMP traffic to an affected device. A successful exploit could allow the attacker to cause memory exhaustion, resulting in instability of other processes, including interior and exterior routing protocols.

Critical Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. Successful exploitation can cause memory exhaustion leading to denial of service conditions affecting critical routing infrastructure.

Affected Products

• Cisco IOS XR Software (version 6.4.2 and potentially others)
• Cisco ASR 9001, ASR 9006, ASR 9010 Routers
• Cisco ASR 9901, ASR 9904, ASR 9906 Routers
• Cisco ASR 9910, ASR 9912, ASR 9922 Routers

Discovery Timeline

• August 29, 2020 - CVE-2020-3566 published to NVD
• October 28, 2025 - Last updated in NVD database

Technical Details for CVE-2020-3566

Vulnerability Analysis

This resource exhaustion vulnerability (CWE-400, CWE-770) exists within the DVMRP implementation in Cisco IOS XR Software. The core issue stems from insufficient queue management mechanisms when handling IGMP packets. When the affected device receives a high volume of specially crafted IGMP traffic, the inadequate queue management fails to properly limit or handle the incoming packets, leading to progressive memory consumption.

The vulnerability affects devices where multicast routing is enabled, particularly those running the DVMRP feature. Since this targets fundamental routing infrastructure, successful exploitation can have cascading effects on network availability and routing stability.

Root Cause

The root cause of CVE-2020-3566 is insufficient queue management for IGMP packets within the DVMRP feature implementation. The software fails to implement proper resource allocation limits when processing IGMP traffic, allowing an attacker to consume available process memory by flooding the device with crafted packets. This represents an uncontrolled resource consumption weakness (CWE-770) where the application does not properly restrict the size or number of resources that are requested or influenced by an actor.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker needs only network access to send crafted IGMP traffic to a vulnerable Cisco IOS XR device. The attack methodology involves:

1. Identifying target devices running vulnerable versions of Cisco IOS XR with multicast routing enabled
2. Crafting malicious IGMP packets designed to trigger excessive memory consumption
3. Flooding the target device with these crafted packets
4. Exhausting process memory, causing instability in routing protocols and other critical processes

The exploitation does not require valid credentials or privileged access, making it particularly dangerous for internet-facing routing infrastructure. The attack causes high availability impact while not affecting confidentiality or integrity of the system.

Detection Methods for CVE-2020-3566

Indicators of Compromise

• Unusual spikes in IGMP traffic volume targeting affected Cisco routers
• Memory utilization anomalies on Cisco IOS XR devices, particularly in IGMP-related processes
• Instability or unexpected restarts of interior and exterior routing protocols (BGP, OSPF, IS-IS)
• System logs indicating memory exhaustion or process failures on ASR 9000 series routers

Detection Strategies

• Monitor IGMP packet rates and volumes using network flow analysis tools to detect anomalous traffic patterns
• Implement SNMP monitoring for memory utilization thresholds on Cisco IOS XR devices with alerts for abnormal consumption
• Deploy network-based intrusion detection systems (NIDS) with signatures for malformed or excessive IGMP traffic
• Configure logging and alerting for routing protocol instability events that may indicate ongoing exploitation

Monitoring Recommendations

• Establish baseline metrics for normal IGMP traffic patterns and memory utilization on vulnerable devices
• Implement real-time monitoring of process memory consumption using Cisco IOS XR show commands such as show memory summary
• Configure SNMP traps for memory threshold violations and routing protocol state changes
• Review system logs regularly for IGMP processing errors or resource exhaustion warnings

How to Mitigate CVE-2020-3566

Immediate Actions Required

• Apply vendor patches as soon as they become available from Cisco
• Implement rate limiting for IGMP traffic at network perimeters to reduce exposure
• Review and disable DVMRP and multicast routing features on devices where they are not required
• Apply access control lists (ACLs) to restrict IGMP traffic to trusted sources only

Patch Information

Cisco has released software updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for detailed patching instructions and the latest fixed software versions. Given that this vulnerability is listed in the CISA Known Exploited Vulnerabilities catalog, prioritize patching as a critical remediation activity.

Workarounds

• Disable IGMP routing if multicast functionality is not required using interface configuration commands
• Implement rate limiting for IGMP traffic to mitigate the impact of exploitation attempts
• Deploy access control lists to filter IGMP traffic from untrusted sources
• Consider implementing Control Plane Policing (CoPP) to protect the router's control plane from excessive traffic

# Example: Disable IGMP on an interface (IOS XR)
configure terminal
interface GigabitEthernet0/0/0/0
 no router igmp
commit

# Example: Implement rate limiting for IGMP (CoPP)
configure terminal
control-plane
 management-plane
  inband
   interface all
    allow IGMP rate 100
commit