Exploited CVEs / Cisco / CVE-2020-3118

CVE-2020-3118

Cisco IOS XR Software Discovery Protocol Format String 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.

Risk summary

HighCISA KEV

8.8

CVSS v3 base

12%

EPSS exploit probability

High

Severity

2021-11-03

Added to KEV

2022-05-03 (past due)

CISA due date

Actively exploited Cisco IOS XR vulnerability, High severity, CVSS v3 8.8. Added to the CISA KEV catalog 2021-11-03.

Senserva AI read on CVE-2020-3118 CISA required action Official fix for CVE-2020-3118 Admin questions

Senserva AI Opinion for CVE-2020-3118

This is a format string flaw in how Cisco IOS XR parses Cisco Discovery Protocol fields, so an unauthenticated attacker on an adjacent Layer 2 segment can run code with admin privileges or crash the device by reloading it. CDP is enabled by default on many interfaces, meaning any exposed IOS XR router or switch reachable at the link layer is at risk. CISA confirmed active exploitation and added it to KEV on 2021-11-03, and with Severity High (CVSS 8.8) the adjacent access requirement is the only real barrier.

Do this: Patch affected Cisco IOS XR devices now, and where patching lags, disable CDP on untrusted or edge-facing interfaces to remove the attack surface.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2020-3118

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I run IT security. Facts for CVE-2020-3118, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2020-3118.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed once a day (early morning US Central)):
- CVE-2020-3118: Cisco IOS XR Software Discovery Protocol Format String Vulnerability
- Affected: Cisco IOS XR
- Severity: High, CVSS v3 8.8; EPSS 30-day exploitation probability 12%
- Added to CISA KEV: 2021-11-03; federal remediation due 2022-05-03
- Ransomware-linked: no
- CISA required action: Apply updates per vendor instructions.
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) The fastest safe path to remediation. 4) How to check whether my environment is exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch now

Exploited in the wild: confirmed by the CISA KEV catalog, not predicted.

The fix ships from the vendor: Cisco Security Advisories (PSIRT).

Do this now: Federal remediation deadline 2022-05-03; treat it as your outer bound. Patch now and verify deployment on every exposed device.

Updated September 3, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2020-3118

Published: 2021-11-03
Last revised: 2021-11-03
Changes tracked: 1

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.

Senserva Watchevery change we have recorded for this one

What changed, and when

2021-11-03 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 8.8; EPSS first scored at 11.7%

Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.

CISA required action

Federal (BOD 22-01) remediation due date: 2022-05-03 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2020-3118

The authoritative fix and affected-version list are published by the vendor. Find the IOS XR advisory on Cisco Security Advisories (PSIRT).

Cisco Security Advisories (PSIRT)CISA KEV entry

Common questions about CVE-2020-3118

Is CVE-2020-3118 actively exploited?

Yes. CVE-2020-3118 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 12%.

What is the CISA deadline and required action for CVE-2020-3118?

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-2020-3118?

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-2020-3118?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2020-3118'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 once a day (early morning US Central).

Scope and sources

More exploited Cisco CVEs: CVE-2026-20349 CVE-2026-20316 CVE-2008-4128 CVE-2026-20230 CVE-2026-20262 CVE-2026-20245 CVE-2026-20182 CVE-2026-20133
All Cisco exploited CVEs on one page: Cisco vulnerabilities actively exploited.
Authoritative references: CVE record NVD detail CISA KEV catalog FIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.