vciy

CVE-2021-38666

INDEX BUILT · 2026-09-20

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Remote Desktop Client Remote Code Execution Vulnerability

CVE-2021-386664 of 4 sources documented this
44

rank 44 = 17 + 17 + 2 + 8 + 0

rank@v1 · scheduled

Someone is already using it

CISA KEV catalog · public proof-of-concept · FIRST EPSS

EPSS 0.15064  ·  without this subject the record ranks 27

What it costs you if it fires

NVD CVSS base score, then the CNA's own

CVSS 6.8, from NVD  ·  without this subject the record ranks 27

It is getting worse, not staying still

FIRST EPSS series, rescorings and bad loads removed

rose on 2026-04-03  ·  without this subject the record ranks 42

How much of the world it touches

NVD CPE configurations

10 products in the CPE ranges  ·  without this subject the record ranks 36

Someone else already set the date

CISA KEV remediation due date

no CISA due date  ·  without this subject the record ranks 44

Unaudited dollar value2 of 3 inputs carry a receipt
Exposure$752,000over the next 30 days, if this record is yours
Movement-$596,000on 2025-02-26, the last material move, 1 year, 6 months before this reading
Basisassumeda published average, not your estate

$752,000 = $4.99M incident cost x 1 exposure x 0.15064 likelihood

udv@v1 · unaudited · wrong for you until you say what you run

$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.

Hindsight · the state

0.15064EPSSNOT IN KEVas of 2026-09-20
Severity8.8 HIGHreceipt
Harmtotal lossreceipt
Exploitationpublic proof-of-conceptreceipt
Defensefix version namedreceipt
Movementdoubled within 72hreceipt
PLATEAU10Minimal movement since 2026-06-15, 80 days at 0.15, as of 2026-09-03. arc-rules@v1

Foresight · where to check next

No weakness class or product neighbourhood is held for this record, so this index cannot name anywhere to check next. That is an absence in the record, not a finding about the software.

Color is a claim, not decoration:the hostile worldthe defenseno signal

Sources disagree here.

Severity score
Microsoft8.8 HIGHreceipt
NVD6.8 MEDIUMreceipt
Scoring standard
MicrosoftCVSS v3.1receipt
NVDCVSS v2.0receipt

Both shown, dated. We don't pick winners. disagreement-rules@v1

Running Microsoft Remote Desktop client for…? Check your version

A deterministic range check against the ranges this record publishes. It tells you where a version sits in the record, not whether your deployment is exploitable. No account needed.

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Harm, if it fires from the vector and the weakness

Written for the ticket you're about to file.

Reachnetwork-reachable · no privileges required · user interaction required · low attack complexityreceipt
ImpactComplete confidentiality, integrity and availability lossreceipt
Scored fromCVSS v3.1 · the CNA's vectorreceipt
Weakness classNo CWE mapping in held sources.

CISA KEV & Federal Remediation Deadline from the record and CISA

The fix, and how long it's been waiting.

Fixed in10.0.10240.19119; 10.0.14393.4770; 10.0.17763.2300; 10.0.18363.1916; 10.0.19041.1348; 10.0.19042.1348; 10.0.19043.1348; 10.0.22000.318; 6.1.7601.25769…receipt
Patch available sinceNo dated patch-availability record in held sources. The index holds reference URLs without dates and only the current revision of the CVE record, so the day a fix first existed cannot be derived. Only the versions it landed in.

Exploit Status & Known PoCs a ladder, not a score

Current rung: Proof-of-concept published · 2 public repositories, 2021-11-12.

  • RUNG 1Nothing observed in held sources
  • RUNG 2Proof-of-concept published · 2 public repositories2021-11-12receipt
  • RUNG 3Exploited in the wild · CISA KEV listed
  • RUNG 4Ransomware campaign use known

Authority who says so

CVSS, the CNA8.8 HIGHreceipt
CVSS, NVD6.8 MEDIUMreceipt
Exploit probability0.15064 · top 3% of all CVEsreceipt
Blast breadth2 products across 1 vendorderived
Assigned bymicrosoftreceipt
Recorded changes65 · last 19 Sep 2026derived

Affected & Fixed Versions as published

Affected productMicrosoft Remote Desktop client for Windows Desktop; Microsoft Windows 10 Version 1507; Microsoft Windows 10 Version 1607; Microsoft Windows 10 Version 1809; Microsoft Windows 10 Version 1909…receipt
Published rangesmicrosoft windows 10 20h2; microsoft windows 10 21h1; microsoft windows 10 1607; microsoft windows 10 1809receipt
Show all 10 published ranges
microsoft windows 10 20h2
microsoft windows 10 21h1
microsoft windows 10 1607
microsoft windows 10 1809
microsoft windows 10 1909
microsoft windows 10 2004
microsoft windows server 2008 r2
microsoft windows server 2012 r2
microsoft windows server 2016 20h2
microsoft windows server 2016 2004
Fixed in10.0.10240.19119; 10.0.14393.4770; 10.0.17763.2300; 10.0.18363.1916; 10.0.19041.1348; 10.0.19042.1348; 10.0.19043.1348; 10.0.22000.318; 6.1.7601.25769…receipt

A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.

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What it is stated by the CNA

Remote Desktop Client Remote Code Execution Vulnerability receipt

NVD's analysis a second authority

severity
6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
affected versions
microsoft windows 10 20h2; microsoft windows 10 21h1; microsoft windows 10 1607; and 7 more, listed in full below
also scored by
[email protected] 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H · [email protected] 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

The CNA scored it 8.8 and NVD 6.8. Both are shown because both were published; we do not pick one.

check it yourself msrc.microsoft.com receipt

Dated events

2021-11-11EPSS moved 0.01 to 0.102025-03-17EPSS moved 0.02 to 0.262026-06-15EPSS moved 0.32 to 0.13

Movement the material steps

10 Nov 20210.00918
6 Jan 20220.32208 · crossed 0.10
1 Apr 20220.01601 · crossed 0.10
7 Mar 20230.0159 · scoring model v2023.03.01
17 Dec 20240.27005 · crossed 0.10
27 Dec 20240.09764 · crossed 0.10
11 Jan 20250.14974 · crossed 0.10
27 Jan 20250.08335 · crossed 0.10
11 Feb 20250.13934 · crossed 0.10
26 Feb 20250.01981 · crossed 0.10
17 Mar 20250.25885 · crossed 0.10 · scoring model v2025.03.14
19 Mar 20250.43583
20 Mar 20250.25885
27 Mar 20250.43583
28 Mar 20250.25885
29 Mar 20250.43583
30 Mar 20250.25885
18 Nov 20250.46816
21 Nov 20250.24616
15 Jun 20260.12993 · scoring model v2026.06.15
3 Sep 20260.15064

This score more than doubled inside 72 hours. Both observations are in the full history below.

Show all 62 observations
10 Nov 20210.00918
11 Nov 20210.09575
6 Jan 20220.32208
4 Feb 20220.2224
1 Apr 20220.01601
28 Jan 20230.01728
7 Mar 20230.0159
8 Mar 20230.01590
22 Apr 20230.01414
5 May 20230.01511
2 Jun 20230.01445
17 Jun 20230.01512
14 Aug 20230.01470
29 Aug 20230.01676
25 Oct 20230.01608
6 Dec 20230.02000
20 Dec 20230.02318
1 Feb 20240.02127
14 Feb 20240.02865
13 Mar 20240.03588
28 Mar 20240.04512
24 Apr 20240.06322
8 May 20240.04927
16 Jun 20240.05252
26 Jul 20240.06417
21 Aug 20240.05216
16 Oct 20240.05488
13 Dec 20240.07174
17 Dec 20240.27005
27 Dec 20240.09764
11 Jan 20250.14974
27 Jan 20250.08335
11 Feb 20250.13934
26 Feb 20250.01981
15 Mar 20250.01749
17 Mar 20250.25885
19 Mar 20250.43583
20 Mar 20250.25885
27 Mar 20250.43583
28 Mar 20250.25885
29 Mar 20250.43583
30 Mar 20250.25885
10 May 20250.26418
11 Jun 20250.23762
16 Jun 20250.24022
16 Aug 20250.18948
1 Oct 20250.24352
27 Oct 20250.18948
28 Oct 20250.24352
15 Nov 20250.24616
18 Nov 20250.46816
21 Nov 20250.24616
27 Dec 20250.16625
28 Dec 20250.21581
18 Feb 20260.22978
28 Feb 20260.21581
3 Apr 20260.31882
15 Jun 20260.12993
26 Jun 20260.1305
6 Jul 20260.12947
20 Aug 20260.1375
3 Sep 20260.15064

62 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt

The full biography

EPSS 0.15064Published2021-11-10Public PoC2021-11-12Index as of2026-09-03

Exploit probability more than doubled between 2021-11-10 and 2021-11-11 (0.00918 → 0.09575) and the record had been public for 4 years, 9 months when this index was last written.

Published 2021-11-10 receipt · Public PoC 2021-11-12 receipt · Index as of 2026-09-03 derived

Siblings and hubs

Records related to this one

Its defect family

microsoft remote desktop client for windows desktop

Of the 3 records in this family, this is the only one holding a stated fix version: 10.0.10240.19119; 10.0.14393.4770; 10.0.17763.2300; 10.0.183.

Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.

Family membership: held values

This record is one of a group, and the group's page describes all of them. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.

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What usually comes next

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