Exploited CVEs / SolarWinds / CVE-2021-35211

CVE-2021-35211

SolarWinds Serv-U Remote Code Execution Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted, and the vulnerability is known to be used in ransomware campaigns. Federal agencies were required to remediate by 2021-11-17 (that deadline has passed); treat that date as the outer bound for your own environment. Check the vendor security advisory for the fix.

Risk summary

CriticalCISA KEVRansomware

10.0

CVSS base

91%

EPSS exploit probability

Critical

Severity

2021-11-03

Added to KEV

2021-11-17 (past due)

CISA due date

Actively exploited SolarWinds Serv-U vulnerability, Critical severity, CVSS 10.0. Added to the CISA KEV catalog 2021-11-03.

Senserva AI read on CVE-2021-35211 CISA required action Official fix for CVE-2021-35211 Admin questions

Senserva AI Opinion for CVE-2021-35211

SolarWinds Serv-U file transfer servers carry this Critical CVSS 10.0 memory escape flaw, exploited in the wild and used in ransomware campaigns. File transfer infrastructure is a repeat ransomware target because it faces the internet and holds business data in transit. A 91 percent EPSS probability years after disclosure shows attackers still find vulnerable Serv-U instances worth hunting.

Do this: Upgrade every Serv-U instance past the CVE-2021-35211 fix today, or take unpatched ones off the internet until you can.

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

Senserva AI Opinion and rich prompt for CVE-2021-35211

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

I run IT security. Facts for CVE-2021-35211, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2021-35211.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2021-35211: SolarWinds Serv-U Remote Code Execution Vulnerability
- Affected: SolarWinds Serv-U
- Severity: Critical, CVSS 10.0; EPSS 30-day exploitation probability 91%
- Added to CISA KEV: 2021-11-03; federal remediation due 2021-11-17
- Ransomware-linked: YES
- 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 immediately

Exploited in the wild and used in ransomware campaigns.

No vendor fix is mapped yet. This page refreshes daily and will name the patch the day one is published.

Do this now: Move this ahead of everything else in the queue, then verify the fix actually landed on every exposed device.

Updated August 14, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2021-35211

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 10.0; EPSS first scored at 91.2%

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: 2021-11-17 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2021-35211

Check the vendor's security advisory channel for the patched Serv-U versions and workarounds.

CISA KEV entry

Common questions about CVE-2021-35211

Is CVE-2021-35211 actively exploited?

Yes. CVE-2021-35211 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 91%. CISA also reports it is known to be used in ransomware campaigns.

What is the CISA deadline and required action for CVE-2021-35211?

CISA set the federal (BOD 22-01) remediation due date at 2021-11-17, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.

What fixes CVE-2021-35211?

Check the vendor's security advisory for the patched Serv-U 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-2021-35211?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2021-35211'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).

Scope and sources

More exploited SolarWinds CVEs: CVE-2026-28318 CVE-2025-26399 CVE-2025-40536 CVE-2025-40551 CVE-2024-28987 CVE-2024-28986 CVE-2024-28995 CVE-2021-35247
All SolarWinds exploited CVEs on one page: SolarWinds 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.