CVE-2020-3569: Cisco IOS XR IGMP DoS Vulnerability

CVE-2020-3569 Overview

CVE-2020-3569 is a denial of service vulnerability affecting the Distance Vector Multicast Routing Protocol (DVMRP) feature in Cisco IOS XR Software. This vulnerability allows an unauthenticated, remote attacker to either immediately crash the Internet Group Management Protocol (IGMP) process or cause it to consume available memory until it eventually crashes. The memory consumption can negatively impact other critical processes running on the device, including interior and exterior routing protocols.

The vulnerability stems from incorrect handling of IGMP packets. An attacker can exploit this flaw by sending specially crafted IGMP traffic to an affected device, resulting in service disruption that could cascade to affect network routing stability across enterprise and service provider environments.

Critical Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. The ability to crash routing processes on carrier-grade equipment poses significant risk to network infrastructure availability.

Affected Products

• Cisco IOS XR Software versions 6.1.4, 6.2.3, 6.3.3, 6.4.2, 6.4.3, 6.5.3, 6.6.2, 6.6.3, 7.0.2, 7.1.2, and 7.1.15
• Cisco ASR 9000 Series Aggregation Services Routers (ASR 9000v, 9001, 9006, 9010, 9901, 9903, 9904, 9906, 9910, 9912, 9922)
• Cisco Network Convergence System (NCS) 520, 540, 560, 5001, 5002, 5011, 5501, 5502, 5508, 5516, 6008 Series
• Cisco Carrier Routing System (CRS) platforms including CRS-1, CRS-3, CRS-X variants

Discovery Timeline

• September 23, 2020 - CVE-2020-3569 published to NVD
• October 28, 2025 - Last updated in NVD database

Technical Details for CVE-2020-3569

Vulnerability Analysis

This vulnerability resides in the DVMRP feature implementation within Cisco IOS XR Software. The IGMP process fails to properly validate and handle malformed IGMP packets, leading to two potential exploitation outcomes: immediate process crash or gradual memory exhaustion.

The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-770 (Allocation of Resources Without Limits or Throttling). The attack can be executed remotely over the network without requiring authentication or user interaction. The scope is changed, meaning the vulnerability can impact resources beyond the vulnerable component—specifically, other routing processes that depend on shared memory resources.

When exploited, the IGMP process consumes memory without proper bounds checking or release mechanisms. This uncontrolled allocation eventually exhausts available system memory, causing instability in co-located processes including BGP, OSPF, IS-IS, and other routing protocols critical to network operations.

Root Cause

The root cause of CVE-2020-3569 is improper input validation in the IGMP packet processing code within the DVMRP feature. The affected code path fails to implement proper bounds checking and resource allocation limits when handling incoming IGMP traffic. This allows malformed or specifically crafted packets to trigger either an immediate crash condition through an unhandled exception or a memory leak that progressively consumes system resources.

The lack of throttling mechanisms for IGMP packet processing exacerbates the vulnerability, as attackers can rapidly send malicious traffic to accelerate the memory exhaustion condition.

Attack Vector

The attack vector is network-based, requiring the attacker to send crafted IGMP packets to an interface on an affected device where multicast routing is enabled. The attack does not require:

• Authentication credentials
• User interaction
• Local access to the device

An attacker with network access to the target device can construct IGMP packets that exploit the improper handling in the DVMRP feature. The attack can originate from any network position that can reach the target interface, making it particularly dangerous in service provider environments where edge routers may be exposed to untrusted network segments.

The exploitation results in denial of service through either an immediate IGMP process crash or progressive memory exhaustion that destabilizes the entire routing platform.

Detection Methods for CVE-2020-3569

Indicators of Compromise

• Unexpected IGMP process crashes or restarts observed in system logs
• Gradual increase in memory utilization on Cisco IOS XR devices without corresponding legitimate traffic growth
• Routing protocol instability (BGP, OSPF, IS-IS sessions flapping) coinciding with IGMP process issues
• Presence of unusual or malformed IGMP traffic patterns in network captures

Detection Strategies

• Monitor Cisco IOS XR devices for IGMP process restarts using syslog or SNMP traps with focus on process crash events
• Implement network intrusion detection signatures for anomalous IGMP traffic patterns targeting affected device interfaces
• Configure memory utilization thresholds and alerting on Cisco IOS XR platforms to detect gradual resource exhaustion
• Deploy flow analysis to identify sources generating unexpected volumes of IGMP traffic toward infrastructure devices

Monitoring Recommendations

• Enable detailed logging for the IGMP process on affected Cisco IOS XR devices to capture crash events and memory allocation patterns
• Implement SNMP polling for memory utilization metrics with baseline comparison to detect abnormal consumption
• Configure syslog forwarding to a centralized SIEM for correlation of IGMP-related events across multiple devices
• Establish network traffic baselines for multicast protocols and alert on deviations that could indicate exploitation attempts

How to Mitigate CVE-2020-3569

Immediate Actions Required

• Review the Cisco Security Advisory for detailed guidance and patch availability
• Identify all Cisco IOS XR devices in your environment running affected software versions
• Implement network access controls to restrict IGMP traffic to trusted sources where possible
• Prioritize patching based on device exposure and criticality to network operations

Patch Information

Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory for specific fixed software versions and upgrade paths. Given this vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, federal agencies and critical infrastructure operators should prioritize remediation according to applicable binding operational directives.

The following IOS XR version families are affected and require updates: 6.1.x, 6.2.x, 6.3.x, 6.4.x, 6.5.x, 6.6.x, 7.0.x, and 7.1.x.

Workarounds

• Disable DVMRP on interfaces where multicast routing is not required to eliminate the attack surface
• Implement infrastructure access control lists (iACLs) to restrict IGMP traffic to only necessary and trusted sources
• Configure rate limiting for IGMP traffic on edge interfaces to slow potential exploitation attempts
• Segment network architecture to limit attacker reach to critical routing infrastructure

# Example: Disable DVMRP on an interface (Cisco IOS XR)
# Consult Cisco documentation for your specific platform and configuration
configure terminal
router igmp
 interface GigabitEthernet0/0/0/0
  router disable
 !
commit
end