CVE-2020-3566
Cisco IOS XR Software DVMRP Memory Exhaustion Vulnerability
Description
CVE-2020-3566 is a HIGH severity denial-of-service vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software, classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-770 (Allocation of Resources Without Limits or Throttling). The vulnerability results from insufficient queue management for Internet Group Management Protocol (IGMP) packets, allowing an unauthenticated, remote attacker to exhaust process memory on an affected device. Successful exploitation causes instability in routing processes including interior and exterior routing protocols. With a CVSS 3.1 score of 8.6 and an EPSS score of 0.0505 (89.63rd percentile), this vulnerability represents a significant availability risk. CISA added it to the KEV catalog on November 3, 2021.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:HOpen in CalculatorCWEs
Affected Products
| Vendor | Product | Version |
|---|---|---|
| cisco | ios xr | 6.4.2 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
References
Weakness Type
CWE-400: Uncontrolled Resource Consumption
Uncontrolled Resource Consumption occurs when software does not properly control the allocation and maintenance of a limited resource, allowing an attacker to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This category encompasses various forms of resource exhaustion including memory exhaustion, CPU exhaustion, disk space exhaustion, and network bandwidth consumption. The lack of proper rate limiting or resource allocation controls allows external actors to consume resources far beyond what is necessary for legitimate operations.
In the context of CVE-2020-3566, the DVMRP feature in Cisco IOS XR Software implements insufficient queue management for IGMP packets. When the router receives a high volume of crafted IGMP traffic, the IGMP process allocates memory for each incoming packet without enforcing limits on the total memory consumption. This allows an attacker to send a sustained stream of crafted IGMP packets that progressively consume all available process memory. As memory is exhausted, the IGMP process becomes unstable and eventually crashes, and the memory pressure can cascade to affect other critical routing processes running on the same device.
Learn more: CWE-400 — Uncontrolled Resource Consumption
Impact Analysis
CVE-2020-3566 carries a CVSS 3.1 base score of 8.6 (HIGH) with network-exploitable attack characteristics and a Changed scope.
Confidentiality (None): This vulnerability does not directly expose confidential information. The attack targets the availability of routing processes rather than data extraction.
Integrity (None): The vulnerability does not allow modification of device configurations or routing data. The impact is limited to resource exhaustion causing service disruption.
Availability (High): The primary impact is severe availability degradation. Memory exhaustion in the IGMP process cascades to affect other processes on the device, including interior routing protocols (OSPF, IS-IS) and exterior routing protocols (BGP). When these routing processes become unstable, the device can no longer maintain routing adjacencies, leading to route flapping and convergence issues that affect the entire network fabric.
Scope (Changed): The CVSS scope is Changed, indicating that the vulnerability in the IGMP/DVMRP process impacts resources beyond its own security context. The memory exhaustion affects the overall device stability and can disrupt routing processes that serve networks far beyond the directly targeted device. In service provider environments, a single affected IOS XR router can cause widespread routing instability across multiple autonomous systems and customer networks.
Exploit Maturity
Active Exploitation: CVE-2020-3566 is actively exploited in the wild. CISA added this vulnerability to the Known Exploited Vulnerabilities catalog on November 3, 2021, with a remediation deadline of May 3, 2022. Cisco's initial advisory acknowledged that the company was aware of active exploitation attempts.
Zero-Day Disclosure: This vulnerability was initially disclosed by Cisco on August 29, 2020 as an actively exploited zero-day before patches were available. Cisco provided interim mitigation guidance while developing software updates, highlighting the urgency of the threat.
Low Exploitation Complexity: The attack requires only the ability to send crafted IGMP packets to an affected device. IGMP is a standard multicast protocol, and crafting malicious packets requires minimal technical sophistication. No authentication or special access is needed.
EPSS Context: The EPSS score of 0.0505 (89.63rd percentile) indicates a high probability of exploitation, consistent with the confirmed active exploitation and low attack complexity.
Broad Attack Surface: Any IOS XR device with multicast routing enabled and an interface receiving IGMP traffic is potentially vulnerable. Multicast routing is widely deployed in service provider and large enterprise networks.
Remediation
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Apply Cisco IOS XR software updates. Install the patched versions as described in Cisco Security Advisory cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz. The update implements proper queue management for IGMP packets.
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Implement IGMP rate limiting as an interim mitigation. If immediate patching is not possible, configure IGMP rate limiting on affected interfaces to restrict the rate of incoming IGMP packets and reduce the memory exhaustion impact.
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Disable DVMRP on interfaces where multicast is not needed. Reduce the attack surface by disabling multicast routing on interfaces that do not require it. Use access control lists to restrict IGMP traffic to authorized sources.
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Deploy infrastructure access control lists. Implement ACLs on device interfaces to filter IGMP traffic from untrusted sources. Permit IGMP only from known multicast sources and rendezvous points.
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Monitor device memory utilization. Set up SNMP or streaming telemetry alerts for abnormal memory consumption patterns on IOS XR devices, particularly in the IGMP and routing processes. Early detection of memory exhaustion can trigger automated response procedures.
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Implement routing protocol resilience. Configure BGP and IGP graceful restart and BFD timers to minimize the impact of process restarts caused by memory exhaustion. This helps maintain routing adjacencies during recovery.
Technical Details
CVE-2020-3566 is a memory exhaustion vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software. DVMRP is a multicast routing protocol, and the vulnerability specifically affects the Internet Group Management Protocol (IGMP) packet processing component that supports DVMRP operations.
The vulnerability exists because the IGMP process does not implement proper queue management or memory allocation limits when processing incoming IGMP packets. Under normal operation, the IGMP process receives and processes multicast group membership messages from hosts and other routers. However, when an attacker sends a high volume of crafted IGMP packets, the process allocates memory for each packet without throttling, leading to progressive memory consumption.
The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H) indicates a network-based attack with low complexity, requiring no privileges or user interaction, and with a Changed scope that reflects the cascading impact on other routing processes. The Changed scope is critical because the IGMP memory exhaustion does not just crash the IGMP process — it destabilizes the entire routing stack on the device.
As the IGMP process consumes available memory, other processes competing for the same memory pool are starved. This includes BGP, OSPF, IS-IS, and LDP processes that maintain routing adjacencies and label switching paths. When these processes cannot allocate memory for keepalive messages or routing updates, adjacencies drop and routes are withdrawn, causing network-wide convergence events.
Cisco disclosed this vulnerability on August 29, 2020 as an actively exploited zero-day, releasing interim mitigations before patches were available. The affected product is Cisco IOS XR version 6.4.2 and other versions where DVMRP multicast routing is enabled.
Frequently Asked Questions
Is CVE-2020-3566 being actively exploited?
Yes, CVE-2020-3566 is actively exploited in the wild. Cisco disclosed it as an actively exploited zero-day on August 29, 2020, before patches were available. CISA subsequently added it to the Known Exploited Vulnerabilities catalog on November 3, 2021. The low complexity of the attack and the availability of detailed technical information make this vulnerability accessible to a wide range of threat actors.
What products are affected by CVE-2020-3566?
CVE-2020-3566 affects Cisco devices running IOS XR Software with the DVMRP multicast routing feature enabled. The vulnerability is confirmed in IOS XR version 6.4.2 and other versions with multicast routing active. IOS XR is deployed on Cisco service provider routers including the ASR 9000, NCS 5500, and CRS series. Any device with an interface processing IGMP traffic is potentially vulnerable.
How do I fix CVE-2020-3566?
Apply the Cisco IOS XR software update from the security advisory. As interim mitigations, implement IGMP rate limiting on affected interfaces, disable DVMRP on interfaces that do not require multicast routing, and deploy access control lists to filter IGMP traffic from untrusted sources. Monitor device memory utilization to detect exploitation attempts early.
How severe is CVE-2020-3566?
CVE-2020-3566 is rated HIGH with a CVSS score of 8.6 and a Changed scope, meaning the memory exhaustion cascades beyond the IGMP process to affect other routing protocols on the device. This can cause widespread routing instability in service provider and enterprise networks. The vulnerability was disclosed as an actively exploited zero-day, underscoring its real-world severity.
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