Exploited CVEs / Cisco / CVE-2020-3566
CVE-2020-3566
Cisco IOS XR Software DVMRP Memory Exhaustion Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted. Federal agencies were required to remediate by 2022-05-03 (that deadline has passed); treat that date as the outer bound for your own environment. The fix is in the vendor advisory: Cisco Security Advisories (PSIRT), linked below.
Actively exploited Cisco IOS XR vulnerability, High severity, CVSS 8.6. Added to the CISA KEV catalog 2021-11-03.
Risk summary
Updated July 27, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.
Senserva AI Opinion for CVE-2020-3566
This is a memory exhaustion flaw in how Cisco IOS XR handles IGMP packets under DVMRP, letting an unauthenticated remote attacker crash the IGMP process or slowly starve the router of memory. Exposure is limited to IOS XR devices with multicast routing enabled, but Cisco disclosed this after seeing real exploitation attempts, and CISA confirmed active exploitation. It matters because a memory leak on a core router degrades over time and can knock out multicast services or the device before anyone notices.
Do this: Check which IOS XR routers have multicast routing active and apply Cisco's fix, or use the interim rate limiting and IGMP access control mitigations until you can patch.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2020-3566
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for CVE-2020-3566
Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.
CISA required action
Federal (BOD 22-01) remediation due date: 2022-05-03 (past due).
Apply updates per vendor instructions.
Official fix for CVE-2020-3566
The authoritative fix and affected-version list are published by the vendor. Find the IOS XR advisory on Cisco Security Advisories (PSIRT).
Common questions about CVE-2020-3566
Is CVE-2020-3566 actively exploited?
Yes. CVE-2020-3566 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 3.6%.
What is the CISA deadline and required action for CVE-2020-3566?
CISA set the federal (BOD 22-01) remediation due date at 2022-05-03, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.
What fixes CVE-2020-3566?
The authoritative fix is in the vendor advisory: see Cisco Security Advisories (PSIRT) for the patched IOS XR versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.
Can I ask my own AI about CVE-2020-3566?
Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2020-3566's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).
More exploited Cisco CVEs
The newest Cisco entries on the CISA KEV catalog:
All Cisco exploited CVEs on one page: Cisco vulnerabilities actively exploited.
Authoritative references
Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.
