Cisco IOS XR DVMRP Memory Exhaustion and Denial of Service Vulnerability (CVE-2020-3566)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS XR Software with the Distance Vector Multicast Routing Protocol (DVMRP) feature enabled
Unauthenticated, remote attackers can cause complete memory exhaustion, leading to instability or crash of critical routing protocols and system processes (Denial of Service)
Apply official Cisco software updates immediately, or implement temporary workarounds such as infrastructure ACLs to rate-limit or block unauthorized IGMP traffic
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Cisco has released software updates to address this vulnerability. Administrators should verify their current software version and apply the appropriate SMU or upgrade to a fixed release.
# Verify current active packages and IOS XR version
show install active
show version
# Example of adding and activating a Cisco SMU patch via TFTP
install add tftp://10.1.1.10/iosxr-k9sec-p.smu
install activate disk0:iosxr-k9sec-p.smu
install commit2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, implement infrastructure Access Control Lists (iACLs) to block or rate-limit IGMP traffic from untrusted sources, or disable multicast routing on vulnerable interfaces.
# Define and apply an ACL to drop unauthorized IGMP traffic
ipv4 access-list block-igmp
deny igmp any any
permit ip any any
!
interface GigabitEthernet0/0/0/0
ipv4 access-group block-igmp ingress
!
# Disable IGMP/Multicast routing on non-essential interfaces
multicast-routing
address-family ipv4
interface GigabitEthernet0/0/0/0
disable
!
!3. Log Audit & IoC Verification Commands
Monitor system memory consumption and IGMP process statistics regularly to detect potential exploitation attempts or memory leaks.
# Check overall system memory and specific process memory usage
show memory summary
show processes memory detail | include igmp
# Monitor IGMP traffic statistics and drop counters
show igmp traffic
show logging | include -ERR|MEM|IGMPStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-3566) exists in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software. The root cause is insufficient queue management when processing Internet Group Management Protocol (IGMP) packets. When the system receives a high volume of crafted IGMP packets, it fails to properly manage the queue and release allocated memory buffers, leading to a progressive memory leak and eventual exhaustion.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated, remote attacker can exploit this vulnerability by transmitting specially crafted IGMP traffic directly to an interface of an affected device. Because the vulnerability lies in the low-level packet handling queue of the DVMRP process, the target device attempts to process every incoming malicious packet, consuming control-plane memory. No authentication or user interaction is required, making the attack highly reliable and easy to execute remotely.
3. Infrastructure & Business Impact
Once memory exhaustion occurs, critical system processes on the Cisco IOS XR device become unstable. This includes not only multicast routing but also essential interior and exterior gateway routing protocols (such as OSPF, IS-IS, and BGP). The failure of these protocols leads to routing table collapse, packet drops, and widespread network outages. Given that this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses an immediate threat to enterprise and service provider infrastructures.
Official Vendor Advisories & References
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. These processes may include, but are not limited to, interior and exterior routing protocols. Cisco will release software updates that address this vulnerability.
Frequently Asked SecOps Questions (CVE-2020-3566)
FAQQ1. How critical is CVE-2020-3566 and is it actively exploited in the wild?
CVE-2020-3566 is rated CVSS 8.6 (HIGH) with a 30-day EPSS exploitation probability of 3.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-3566?
Primary impacted vendors include cisco across ios xr. Scope summary: All versions of Cisco IOS XR Software where the DVMRP feature is enabled and configured to receive IGMP packets
Q3. What temporary mitigations or workarounds exist for CVE-2020-3566 before patching?
[Mitigation] Apply official Cisco software updates immediately, or implement temporary workarounds such as infrastructure ACLs to rate-limit or block unauthorized IGMP traffic Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2020-3566
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (cisco)
View Category →Cisco Identity Services Engine (ISE) Critical Authentication Bypass Vulnerability (CVE-2026-76460)
[Affected Scope] Cisco Identity Services Engine (ISE) web-based management interface and API endpoints.
Cisco Catalyst SD-WAN Peering Authentication Bypass Vulnerability (CVE-2026-20182)
[Affected Scope] Cisco Catalyst SD-WAN Controller (formerly vSmart), Manager (formerly vManage), and Validator (formerly vBond)
Cisco Secure Firewall Management Center (FMC) Insecure Deserialization Vulnerability (CVE-2026-20131, CVSS 10.0) - Remote Code Execution and Root Privilege Escalation
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software.
Cisco Secure Firewall Management Center (FMC) Authentication Bypass and Root RCE Vulnerability (CVE-2026-20079)
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.