Exploited CVEs / SolarWinds / CVE-2021-35247

CVE-2021-35247

SolarWinds Serv-U Improper Input Validation Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted. Federal agencies were required to remediate by 2022-02-04 (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

MediumCISA KEV

5.3

CVSS base

3.5%

EPSS exploit probability

Medium

Severity

2022-01-21

Added to KEV

2022-02-04 (past due)

CISA due date

Actively exploited SolarWinds Serv-U vulnerability, Medium severity, CVSS 5.3. Added to the CISA KEV catalog 2022-01-21.

Senserva AI read on CVE-2021-35247 CISA required action Official fix for CVE-2021-35247 Admin questions

Senserva AI Opinion for CVE-2021-35247

SolarWinds Serv-U through version 15.2.5 accepts unsanitized query input, an improper input validation issue attackers exploited despite a modest 3% EPSS score and Medium Severity (CVSS 5.3). Its KEV listing is the tell: real campaigns used it, and file transfer servers are consistently attractive because of the data they move. Serv-U instances are commonly internet-facing by design.

Do this: Upgrade Serv-U past version 15.2.5 and review its logs for malformed or unusual login queries.

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

Senserva AI Opinion and rich prompt for CVE-2021-35247

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

I run IT security. Facts for CVE-2021-35247, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2021-35247.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2021-35247: SolarWinds Serv-U Improper Input Validation Vulnerability
- Affected: SolarWinds Serv-U
- Severity: Medium, CVSS 5.3; EPSS 30-day exploitation probability 3.5%
- Added to CISA KEV: 2022-01-21; federal remediation due 2022-02-04
- 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.

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

Do this now: Federal remediation deadline 2022-02-04; treat it as your outer bound. Patch now and verify deployment 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-2021-35247

Published: 2022-01-21
Last revised: 2022-01-21
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

Drawn by Senserva Vivid from the Senserva change record. Hover any point for its date and value.

2022-01-21 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 5.3; EPSS first scored at 3.4%
2026-07-24 EPSS 3.4% to 3.5%
2026-07-27 EPSS 3.5% to 3.4%
2026-08-02 EPSS 3.4% to 3.5%

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: 2022-02-04 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2021-35247

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

CISA KEV entry

Common questions about CVE-2021-35247

Is CVE-2021-35247 actively exploited?

Yes. CVE-2021-35247 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2022-01-21, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 3.5%.

What is the CISA deadline and required action for CVE-2021-35247?

CISA set the federal (BOD 22-01) remediation due date at 2022-02-04, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.

What fixes CVE-2021-35247?

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-2021-35247?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2021-35247'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-2020-10148
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.