CVE-2020-3569: Cisco IOS XR Software DVMRP Memory Exhaustion Vulnerability

CVE-2020-3569 is a memory exhaustion vulnerability in Cisco IOS XR Software related to how the Distance Vector Multicast Routing Protocol (DVMRP) handles Internet Group Management Protocol (IGMP) packets. An unauthenticated, remote attacker could crash the IGMP process immediately or force it to consume available memory until it crashes, disrupting multicast-related services on affected routers.

For network operators running Cisco IOS XR, this matters because it can cause process instability or denial of service without authentication. Confirm exact impact and fixed releases against the vendor advisory.

How it works

This issue falls under CWE-400 (Uncontrolled Resource Consumption). The software incorrectly handles certain IGMP packets in the DVMRP path. An attacker who can send crafted IGMP traffic to a vulnerable device may trigger the IGMP process to crash outright or to allocate memory until resources are exhausted and the process fails.

No authentication is required. The result is a denial-of-service condition against the IGMP process rather than code execution. Specific packet formats and exploit mechanics are not detailed here; treat any public proof-of-concept claims cautiously and validate behavior only in controlled lab conditions against the vendor’s description.

Am I affected? How to find it in your systems

Cisco IOS XR is commonly deployed on service-provider and large-enterprise routers that handle multicast routing. Inventory all devices running IOS XR, especially those with DVMRP or IGMP features enabled or exposed to untrusted networks.

• Use your configuration management database, network inventory tools, or CLI/show commands to list IOS XR versions and whether multicast/IGMP/DVMRP is configured.
• Compare running versions and feature sets against the affected product list in the Cisco advisory for CVE-2020-3569; do not rely on version guesses.
• Check interface and control-plane ACLs to see whether IGMP packets from untrusted sources can reach the device.
• Review logs and telemetry for unexpected IGMP process restarts, memory growth attributed to the IGMP process, or multicast control-plane instability. These signs are not definitive proof of exploitation but warrant investigation.

If public detail on exact vulnerable configurations is limited, treat any IOS XR system that processes IGMP in a DVMRP context as in-scope until the advisory clears it.

How to remediate

Patch first. Apply the updates Cisco provides for this vulnerability, following the vendor instructions referenced in the CISA guidance. Schedule maintenance windows appropriate for production routers and verify the fixed software train after installation.

• Confirm the advisory’s fixed releases and any prerequisite or upgrade path notes before deploying.
• After patching, re-check that IGMP/DVMRP-related processes are stable and that memory utilization returns to baseline.
• As hardening for this class of flaw, restrict who can send IGMP and other multicast control packets to the device (control-plane policing, interface ACLs, and infrastructure ACLs).
• Disable DVMRP or unused multicast features if they are not required in your design.

If you can't patch immediately

Reduce exposure until you can apply the vendor update:

• Segment and filter: block or tightly limit IGMP and related multicast control traffic from untrusted or external networks at upstream firewalls or on the device itself.
• Control-plane protection: apply control-plane policing and receive ACLs so only expected sources can reach IGMP processes.
• Feature disablement: if DVMRP or IGMP is not operationally required, disable it to remove the attack surface.
• Monitoring: alert on IGMP process crashes, rapid memory growth, or unusual IGMP packet rates. Retain logs for later forensics.
• Virtual patching: where a network security device can identify anomalous IGMP patterns described by the vendor, use temporary signatures or rate limits; validate any such rules so legitimate multicast is not broken.

These steps lower risk but do not replace the official software fix.

If your data may have been exposed

This vulnerability is described as a denial-of-service condition against the IGMP process; ransomware use is not documented. Actively exploited network-device flaws can still be a foothold for broader incidents, so verify device integrity, review authentication and configuration changes, and watch for follow-on activity. You can run a free exposure scan of your email addresses against known breach data sets to check whether credentials or personal data associated with your team have appeared in unrelated breaches, then force password resets and enable stronger authentication where needed.