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Microsoft Exchange Server Remote Code Execution Vulnerability
CVE-2021-268584 of 4 sources documented this
rank 71 = 40 + 17 + 3 + 5 + 6
rank@v1 · act now
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.93651 · CISA KEV listed · without this subject the record ranks 31
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 54
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
rose on 2026-04-21 · without this subject the record ranks 68
How much of the world it touches
NVD CPE configurations
3 products in the CPE ranges · without this subject the record ranks 66
Someone else already set the date
CISA KEV remediation due date
CISA remediation date held · without this subject the record ranks 65
Unaudited dollar value2 of 3 inputs carry a receipt
Exposure$4.67Mover the next 30 days, if this record is yours
Movement+$207,000on 2026-08-20, the last material move, 15 days before this reading
Basisassumeda published average, not your estate
$4.67M = $4.99M incident cost x 1 exposure x 0.93651 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.
PLATEAUMinimal movement since 2026-06-15, 81 days at 0.94, as of 2026-09-04. 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
Both shown, dated. We don't pick winners. disagreement-rules@v1
Running Microsoft Exchange Server 2013 Cumulative…? 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.
Watch this record
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Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
Reachneeds local access · no privileges required · user interaction required · low attack complexityreceipt
ImpactComplete confidentiality, integrity and availability lossreceipt
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.
CISA remediation statusoverdue since 2022-05-03receipt
CISA required actionApply updates per vendor instructions.receipt
Published to CISA KEV246 daysderived
Exploit Status & Known PoCs a ladder, not a score
Current rung: Ransomware campaign use known, 2021-11-03.
RUNG 1Nothing observed in held sources
RUNG 2Proof-of-concept published
RUNG 3Exploited in the wild · CISA KEV listed2021-11-03receipt
RUNG 4Ransomware campaign use known2021-11-03receipt
Affected productMicrosoft Exchange Server 2013 Cumulative Update 21; Microsoft Exchange Server 2013 Cumulative Update 22; Microsoft Exchange Server 2013 Cumulative Update 23…receipt
Published rangesmicrosoft exchange server 2013; microsoft exchange server 2016; microsoft exchange server 2019receipt
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.
What it is stated by the CNA
ProxyLogon is the common name for CVE-2021-26858. Microsoft Exchange Server Remote Code Execution Vulnerability cve-aliases@2026-08-27
NVD's analysis a second authority
severity
6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
affected versions
microsoft exchange server 2013; microsoft exchange server 2016; microsoft exchange server 2019
17 Mar 20250.7953 · crossed 0.50 · scoring model v2025.03.14
22 Mar 20250.69374
26 Mar 20250.82925
29 Mar 20250.93892 · crossed 0.90
30 Mar 20250.81232 · crossed 0.90
3 May 20250.67112
10 May 20250.54917
15 May 20250.73303
27 Jun 20250.52363
2 Jul 20250.74291
16 Jul 20250.85758
30 Jul 20250.75176
2 Sep 20250.52539
22 Oct 20250.63488
18 Nov 20250.86249
21 Nov 20250.55064
13 Apr 20260.4984 · crossed 0.50
21 Apr 20260.72393 · crossed 0.50
15 Jun 20260.89509 · scoring model v2026.06.15
20 Aug 20260.93651 · crossed 0.90
Show all 136 observations
14 Apr 20210.32208
4 Feb 20220.17574
21 May 20220.29336
18 Sep 20220.31092
7 Mar 20230.11341
16 Mar 20230.10607
29 Mar 20230.10006
26 Apr 20230.11092
8 May 20230.51655
10 May 20230.48950
25 May 20230.45994
6 Jun 20230.40246
22 Jun 20230.33115
4 Jul 20230.44696
19 Jul 20230.61701
2 Aug 20230.40975
15 Aug 20230.65723
29 Aug 20230.33174
11 Sep 20230.35482
22 Sep 20230.36773
25 Sep 20230.57569
7 Oct 20230.32505
21 Oct 20230.41361
3 Nov 20230.35482
16 Nov 20230.34278
30 Nov 20230.55537
12 Dec 20230.31213
27 Dec 20230.40870
9 Jan 20240.32711
23 Jan 20240.30911
6 Feb 20240.46857
7 Feb 20240.49758
19 Feb 20240.35579
5 Mar 20240.49023
19 Mar 20240.42090
4 Apr 20240.70350
18 Apr 20240.55939
3 May 20240.63114
19 May 20240.56845
3 Jun 20240.61922
18 Jun 20240.22253
5 Jul 20240.16449
20 Jul 20240.16531
5 Aug 20240.15787
22 Aug 20240.18403
9 Sep 20240.17445
27 Sep 20240.15863
14 Oct 20240.15787
17 Dec 20240.15671
20 Dec 20240.15565
17 Mar 20250.7953
19 Mar 20250.79553
20 Mar 20250.76896
21 Mar 20250.75018
22 Mar 20250.69374
26 Mar 20250.82925
27 Mar 20250.81232
29 Mar 20250.93892
30 Mar 20250.81232
2 Apr 20250.77091
15 Apr 20250.79804
23 Apr 20250.77003
24 Apr 20250.78696
29 Apr 20250.79349
1 May 20250.77699
3 May 20250.67112
6 May 20250.5865
10 May 20250.54917
15 May 20250.73303
19 May 20250.73297
23 May 20250.70213
24 May 20250.80586
25 May 20250.81272
26 May 20250.77893
3 Jun 20250.77699
5 Jun 20250.77893
25 Jun 20250.77574
26 Jun 20250.63976
27 Jun 20250.52363
29 Jun 20250.54164
2 Jul 20250.74291
6 Jul 20250.75395
15 Jul 20250.78824
16 Jul 20250.85758
17 Jul 20250.85153
18 Jul 20250.85282
24 Jul 20250.8392
30 Jul 20250.75176
18 Aug 20250.78235
19 Aug 20250.76165
1 Sep 20250.75955
2 Sep 20250.52539
13 Sep 20250.54338
16 Sep 20250.60122
17 Sep 20250.61763
18 Sep 20250.53064
23 Sep 20250.60122
25 Sep 20250.53064
1 Oct 20250.57818
22 Oct 20250.63488
27 Oct 20250.62012
28 Oct 20250.63488
31 Oct 20250.55064
18 Nov 20250.86249
21 Nov 20250.55064
22 Nov 20250.61953
27 Nov 20250.55064
18 Dec 20250.53277
27 Dec 20250.51594
28 Dec 20250.53277
8 Jan 20260.55064
19 Jan 20260.53277
21 Jan 20260.55064
18 Feb 20260.53277
22 Feb 20260.55064
3 Mar 20260.53277
8 Mar 20260.53026
13 Apr 20260.4984
21 Apr 20260.72393
22 Apr 20260.74482
6 May 20260.64032
7 May 20260.69898
8 May 20260.72274
9 May 20260.76304
10 May 20260.78351
11 May 20260.79454
12 May 20260.81854
13 May 20260.79568
19 May 20260.64484
21 May 20260.78845
22 May 20260.79971
25 May 20260.80167
26 May 20260.78109
29 May 20260.73244
15 Jun 20260.89509
20 Aug 20260.93651
136 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
Listed by CISA 246 days after it published and the record had been public for 5 years, 6 months when this index was last written.
No material movement in 15 days as of the last ingest this index recorded.
Published 2021-03-02 receipt · CISA KEV 2021-11-03 receipt · Index as of 2026-09-04 derived