CASCACascade Atlas

Evidence dossier

CVE-2021-26857

Microsoft Exchange Server Remote Code Execution Vulnerability

Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 7.8. EPSS estimates 95.8% exploit likelihood as of Oct 21, 2026.

79.1–92.7Priority evidence range
Evidence through Oct 22, 2026, 6:07 PM UTC

As of Oct 22, 2026

Normalized restatement

Microsoft Exchange Server Remote Code Execution Vulnerability

State
PUBLISHED
Published
Mar 2, 2021
Updated
Aug 19, 2026
Evidence coverage
85%

Evidence chronology

What was known when

Download this view's receipt →
  1. Source dateSource date omittedFirst observed by CASCA
    CISA-ADP

    Record text: CISA ADP Vulnrichment

    Inspect raw assertion
    Field
    container
    Value
    CISA ADP Vulnrichment
    Original evidence ↗
  2. Source dateSource date omittedFirst observed by CASCA
    CVE Program

    Record text: CVE Program Container

    Inspect raw assertion
    Field
    container
    Value
    CVE Program Container
    Original evidence ↗
  3. Source dateSource date omittedFirst observed by CASCA
    microsoft

    Record text: Microsoft Exchange Server Remote Code Execution Vulnerability

    Inspect raw assertion
    Field
    container
    Value
    Microsoft Exchange Server Remote Code Execution Vulnerability
    Original evidence ↗
  4. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Microsoft Exchange Server Remote Code Execution Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Microsoft Exchange Server Remote Code Execution Vulnerability
    Original evidence ↗
  5. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 95.76% probability · 99.87th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.957620000000; percentile 0.998740000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Nov 3, 2021 · first observed Sep 1, 2026

Exploit likelihood95.76%

FIRST EPSS · score date Oct 21, 2026 · 99.9th percentile · first observed Oct 21, 2026

SeverityCVSS 7.8

microsoft · CVSS 3.1 · first observed Aug 19, 2026 · same-version scores align in this snapshot

Evidence detail

Source limits and decisions

Why each evidence state has this value

casca-unknown-reasons-v1
Exploitation statusLast verified source snapshot retained

The last verified source boundary remains in force for this claim.

Revision
evidence-policy-v1.1.0
Cutoff
Oct 22, 2026
Resolution
Review source contract
Exploit likelihoodEvidence supported

Eligible evidence is present for this bounded claim.

Revision
evidence-policy-v1.1.0
Cutoff
Oct 22, 2026
Resolution
None
Severity assessmentEvidence supported

Eligible evidence is present for this bounded claim.

Revision
casca-direct-cvss-eligibility-v1
Cutoff
Oct 22, 2026
Resolution
None
Affected productsSource-reported scope

The cited source assertion is retained while canonical product linkage remains open.

Revision
casca-factor-d-obligations-v1
Cutoff
Oct 22, 2026
Resolution
Resolve identity

Source comparison

Who said what

CISA-ADPIndependent enrichment
Record text

CISA ADP Vulnrichment

Inspect raw assertion
Field
container
Value
CISA ADP Vulnrichment
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CVE ProgramDerivative copy
Record text

CVE Program Container

Inspect raw assertion
Field
container
Value
CVE Program Container
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
microsoftOriginal assertion
Record text

Microsoft Exchange Server Remote Code Execution Vulnerability

Inspect raw assertion
Field
container
Value
Microsoft Exchange Server Remote Code Execution Vulnerability
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CISA KEVOriginal assertion
Exploitation cataloged

Microsoft Exchange Server Remote Code Execution Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Microsoft Exchange Server Remote Code Execution Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

95.76% probability · 99.87th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.957620000000; percentile 0.998740000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
25Underlying assertions
1Canonical products
25Target assertions
0Constraint assertions

Grouped from 1 configuration nodes in this exact snapshot. Visual grouping is navigational; asset exposure and root cause require cited evidence.

Identity source boundaries
  • Cpe dictionary1,775,266 records · observed through 2026-07-21T06:45:29.809Z27d65b0f-b718-4b4f-bb79-c47c68d09dfa
  • Cpe match643,502 records · observed through 2026-07-21T08:13:17.697Z955dae73-7302-438b-aee1-058d7cc5d48e

27 scope groups

microsoft · source assertedMicrosoftMicrosoft Exchange Server 2010 Service Pack 3Direct source scope
Affected: 14.0.0.0 to before 14.03.0513.000 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "14.0.0.0", "lessThan": "14.03.0513.000", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2013 Cumulative Update 21Direct source scope
Affected: 15.00.0 to before 15.00.1395.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1395.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2013 Cumulative Update 22Direct source scope
Affected: 15.00.0 to before 15.00.1473.006 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1473.006", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2013 Cumulative Update 23Direct source scope
Affected: 15.00.0 to before 15.00.1497.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1497.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2013 Service Pack 1Direct source scope
Affected: 15.00.0 to before 15.00.0847.064 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.0847.064", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 10Direct source scope
Affected: 15.01.0 to before 15.01.1531.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1531.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 11Direct source scope
Affected: 15.01.0 to before 15.01.1591.018 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1591.018", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 12Direct source scope
Affected: 15.01.0 to before 15.01.1713.010 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1713.010", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 13Direct source scope
Affected: 15.01.0 to before 15.01.1779.008 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1779.008", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 14Direct source scope
Affected: 15.01.0 to before 15.01.1847.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1847.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 15Direct source scope
Affected: 15.01.0 to before 15.01.1913.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1913.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 16Direct source scope
Affected: 15.01.0 to before 15.01.1979.008 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1979.008", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 17Direct source scope
Affected: 15.01.0 to before 15.01.2044.013 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2044.013", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 18Direct source scope
Affected: 15.01.0 to before 15.01.2106.013 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2106.013", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 19Direct source scope
Affected: 15.01.0 to before 15.01.2176.009 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2176.009", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 8Direct source scope
Affected: 15.01.0 to before 15.01.1415.010 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1415.010", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 9Direct source scope
Affected: 15.01.0 to before 15.01.1466.016 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1466.016", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019Direct source scope
Affected: 15.02.0 to before 15.02.0221.018 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0221.018", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 1Direct source scope
Affected: 15.02.0 to before 15.01.1979.006 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.01.1979.006", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 2Direct source scope
Affected: 15.02.0 to before 15.02.0397.011 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0397.011", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 3Direct source scope
Affected: 15.02.0 to before 15.02.0464.015 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0464.015", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 4Direct source scope
Affected: 15.02.0 to before 15.02.0659.012 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0659.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 5Direct source scope
Affected: 15.02.0 to before 15.02.0595.008 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0595.008", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 6Direct source scope
Affected: 15.02.0 to before 15.02.0529.013 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0529.013", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 7Direct source scope
Affected: 15.02.0 to before 15.02.0721.013 (custom comparison)
Source-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Inspect raw assertion[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0721.013", "versionType": "custom"}]

Affected-product evidence

Accepted scope and product mapping

0 canonical links · 2 source-reported links

Source-reported scopeSource-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Vendor specified only by source · Product specified only by source

Source class
Direct cve affected
Assertions
26
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Oct 22, 2026
Retained assertion IDs
00568139-3ec5-4580-9c8e-d5bb0f0b8d85120d493e-bc60-453b-af43-59ef735d1dd512d99534-021d-4df8-9db6-3991961a3fc91a18188c-7514-4449-b532-8e47a83f38501a8c8008-4aa3-4c52-9995-e7781beb453a2e16a5a9-b522-415c-8202-4271203212bd39af44ed-bf5b-4280-84be-1d793713953839debe37-c486-4853-98b9-6a6f71616bc646fb1121-a7e2-4072-8dfb-723ba97491534933f61b-8e4d-4f0b-97f9-d4b5672575f94c367938-1de8-424a-9afc-5a22e1e9480557a61936-8bea-4f8c-9770-d528da4108356c0dd4b4-429e-4b2e-b4cd-e076797fb1b0763bc321-6783-4b5b-a0b0-b0e69c84e01f7e1e797c-f060-4188-a3ce-f2dfebd21ace8bb296e6-5c45-49c3-b681-9d2a61fd2f78b475d450-9af8-4467-8f46-cbd1aa49d53cbbbd99fe-cd86-4cdf-b706-88afeec35743bee715bf-fa5f-4f5c-9a3c-485d89e29fb8c24fe04e-f4ca-435a-a5da-267b85ccc484d17119d4-635d-4bda-a27a-3b65643ab124d3ff6109-eb24-490d-b4ac-7034a5d36ba3d726fcc0-ec34-404a-acda-924e3f7e7b23dc9370ac-9945-4164-a48c-55e294d741aaea2793ac-9177-4c12-94bc-a55ed4aa1974ef41e11a-cfe2-44fe-8ea6-5330c336df4e
Source-reported scopeSource-reported scope

Canonical linkage remains open; the cited source assertion is retained below.

Vendor specified only by source · Product specified only by source

Source class
Nvd cpe vulnerable target
Assertions
26
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Oct 22, 2026
Retained assertion IDs
0e8a0fe0-009f-404c-85d6-7739fb3a6da50ee03df9-50e6-4735-bbf5-4f00c6c0fb3d1a65279b-96a7-4371-9696-694e0562747524d8f9cf-25eb-4218-b417-8518986d5618391d8f23-91b5-4498-84d6-075f9eaf5df83caeddaf-27ed-48d9-9244-a2d2638ad5303eebea56-b60b-42cf-8e4b-7743b4a2b8834855fb9b-6781-4776-99ad-a292eed090e44b33eb01-a439-41ac-b5a1-a14b9519d6f54d942184-3045-40c2-8651-c40ca43f9fbe5ecccf36-a9a2-45bb-a600-23bb86b654fc64b3d416-fdeb-49c8-8e37-709a84bca22667f044f1-0961-4d2c-9f98-33f97946ae5677c216cc-f553-4990-be1e-801e238f6bf38509c11b-eac1-4091-87f7-5501aa6749b788bedde4-42a7-4679-8bf5-81d878ec293388d9091d-1467-47e9-af03-f7889b49564995a9dd7b-a799-439f-9c64-af314fc9bb299b802d16-7502-4de3-931d-400acf8ae3d69ceb393d-4641-4e36-b3a5-5845f686dc8f9e626fe0-68ec-47dc-8684-14fa259abffcaa532d23-4753-4a5a-bf02-6cf908965479bea90224-801b-4921-aaa6-470533023f60c71a760f-37f3-492c-8799-4db3c6d1a2f3d492c9d6-c1a4-4df7-9918-a69353065299e6e394cd-dea5-4181-babc-3b691d236f1e

Assessments

CVSS by origin

6.8
NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8
NVDCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8
secure@microsoft.comCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8
microsoftCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

Direct CVE/CNA normalized decisions

7.8Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
Validation
Valid match
Recomputed
7.8
Decision reason
Evidence supported
Policy
casca-direct-cvss-eligibility-v1

Assessments are retained side by side under closed precedence. Cascade never averages CVSS.

Evidence boundaries

  • KEV membership is authoritative for the catalog, not proof of exposure in any environment.
  • EPSS is a dated model probability and not an individual-environment prediction.
  • Affected or fixed status applies only to the exact cited product and version scope; remaining scope stays source-scoped.
  • NVD-carried upstream facts remain derivative; independent corroboration requires a separately authored source.
  • Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
  • NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
  • Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.
  • OSV aggregation and OSV-converted NVD material are not independent corroboration.
  • Red Hat facts are vendor assertions for the exact supplied products.
  • Nonmembership and not-yet-observed states are not proof of safety.