CVE-2020-3566: Cisco IOS XR Software DVMRP Memory Exhaustion Vulnerability

CVE-2020-3566 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 functions on affected routers. This matters for network operators because IOS XR commonly runs on service-provider and large enterprise edge and core devices where availability is critical; a successful attack can interrupt routing services without needing credentials.

How it works

The underlying weakness is CWE-400 (Uncontrolled Resource Consumption). According to the CISA summary, Cisco IOS XR’s DVMRP implementation incorrectly handles certain IGMP packets. An attacker who can send crafted IGMP traffic to a vulnerable device may cause the IGMP process either to terminate at once or to allocate memory until resources are exhausted and the process fails. Because the attack is remote and unauthenticated, reachability to the affected service is the primary prerequisite. Exact packet formats, required interface states, or precise trigger conditions are not detailed in the provided facts and must be confirmed against the vendor advisory. The result is a denial-of-service condition against the IGMP process rather than code execution or data theft.

Am I affected? How to find it in your systems

Cisco IOS XR is typically deployed on carrier-grade and large-scale enterprise routers that participate in multicast routing. Inventory every device running IOS XR, paying particular attention to those with DVMRP or IGMP enabled or with multicast routing configured. Compare the installed software release against the fixed versions listed in Cisco’s advisory for CVE-2020-3566; the facts supplied here do not include version numbers, so confirmation against the vendor advisory is required. Check running configuration for DVMRP-related commands and for interfaces that accept IGMP. Review control-plane and process logs for unexpected IGMP process restarts, memory-pressure warnings, or sudden spikes in memory attributed to the IGMP process. Network telemetry showing unusual volumes of IGMP traffic directed at the device can also be an early indicator, though such traffic alone does not prove exploitation.

How to remediate

The primary remediation is to apply the software updates published by Cisco for this vulnerability, following the vendor’s installation and verification instructions. CISA’s required action is simply to apply updates per vendor instructions. After patching, validate that the IGMP process remains stable under normal multicast load and that no residual configuration enables unnecessary DVMRP exposure. As general hardening for this class of resource-consumption issues, restrict which interfaces accept IGMP, apply control-plane policing to limit the rate of IGMP packets, and disable DVMRP or multicast features on devices that do not require them. Document the change window and retain pre- and post-patch configuration snapshots for audit purposes.

If you can't patch immediately

Until the vendor update can be installed, reduce exposure with compensating controls. Segment management and multicast-facing interfaces so that untrusted networks cannot reach the IGMP/DVMRP listeners. Use access-control lists or control-plane policing to drop or rate-limit IGMP packets from untrusted sources. If the feature is not required, disable DVMRP and related multicast services entirely. Consider virtual patching or firewall rules that block anomalous IGMP traffic patterns at the network edge. Increase monitoring of IGMP process health, memory utilization, and crash logs so that any exploitation attempt is detected quickly. These measures lower risk but do not replace the patch.

If your data may have been exposed

Actively exploited vulnerabilities can lead to broader incidents, although ransomware use of this CVE is not documented in the provided facts. The described impact is denial of service against the IGMP process rather than direct data exfiltration; nevertheless, any successful attack on network infrastructure warrants a review of adjacent systems and logs for follow-on activity. Organizations concerned about credential or data exposure from other incidents can run a free exposure scan of their email addresses against known breach data sets to determine whether those identities appear in prior breaches.