CASCACascade Atlas

Evidence dossier

CVE-2021-33766

Microsoft Exchange Server Information Disclosure Vulnerability

Exploited in the wild (CISA KEV since Jan 18, 2022). microsoft reports CVSS 3.1 7.3. EPSS estimates 98.2% exploit likelihood as of Oct 17, 2026.

78.1–87.7Priority evidence range
Evidence through Oct 22, 2026, 6:07 PM UTC

As of Oct 22, 2026

Normalized restatement

Microsoft Exchange Server Information Disclosure Vulnerability

State
PUBLISHED
Published
Jul 14, 2021
Updated
Aug 10, 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 Information Disclosure Vulnerability

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

    Exploitation cataloged: Microsoft Exchange Server Information Disclosure

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Microsoft Exchange Server Information Disclosure
    Original evidence ↗
  5. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 98.18% probability · 99.91th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.981760000000; percentile 0.999150000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Jan 18, 2022 · first observed Sep 1, 2026

Exploit likelihood98.18%

FIRST EPSS · score date Oct 17, 2026 · 99.9th percentile · first observed Oct 17, 2026

SeverityCVSS 7.3

microsoft · CVSS 3.1 · first observed Aug 10, 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 Information Disclosure Vulnerability

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

Microsoft Exchange Server Information Disclosure

Inspect raw assertion
Field
observed_exploitation
Value
Microsoft Exchange Server Information Disclosure
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

98.18% probability · 99.91th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.981760000000; percentile 0.999150000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
5Underlying assertions
1Canonical products
5Target 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

6 scope groups

microsoft · source assertedMicrosoftMicrosoft Exchange Server 2013 Cumulative Update 23Direct source scope
Affected: 15.00.0 to before 15.00.1497.015 (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": "15.00.1497.015", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 19Direct source scope
Affected: 15.01.0 to before 15.01.2176.012 (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": "15.01.2176.012", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2016 Cumulative Update 20Direct source scope
Affected: 15.01.0 to before 15.01.2242.008 (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": "15.01.2242.008", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 8Direct source scope
Affected: 15.02.0 to before 15.02.0792.013 (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": "15.02.0792.013", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Exchange Server 2019 Cumulative Update 9Direct source scope
Affected: 15.02.0 to before 15.02.0858.010 (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": "15.02.0858.010", "versionType": "custom"}]
NVD CPE · APPLICATIONmicrosoftexchange_serverVulnerable target · 5 assertions
Version 2013; Version 2016; Version 2019Canonical identity product-d87daca995d075bf30565cc429e7242a47683272975068df1d327ec1d8ff609cLinked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    28fca0e8-7d27-4746-9731-91b834ca3e64
  2. cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 4
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    71cdf29b-116b-4de2-afd0-b62477ff0aeb
  3. cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 2
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    19c1ee0c-b8dd-4b91-be4b-1c42d72fb718
  4. cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    da166f2a-d83b-4d50-ad0b-668d813e0585
  5. cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 3
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    44ecf39a-1de1-4870-a494-06a53494338d

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
5
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Oct 22, 2026
Retained assertion IDs
5aa62304-c34a-47c6-9b7a-dfb4c180023d7fd701fa-ee60-4eb5-9beb-eebdfaf964d0c7347450-d1ad-4505-a475-f8cb91756f3ccc85de0d-fa98-4f45-a078-30bacb4b62d6fbd69508-6d4c-4219-ac42-be24f5537a68
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
5
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Oct 22, 2026
Retained assertion IDs
0bffb938-5009-40ca-af2b-8b0c501055f52661833f-1fe4-4279-a1a7-1b20c38ad35d60706efe-11a2-428c-a61c-1d19cae2d4a0c4d766fb-2f14-4ddc-9ffc-4b919d292739fc850f67-e1bf-47b4-b52f-fccb6fe656c6

Assessments

CVSS by origin

5.0
NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:N/AC:L/Au:N/C:P/I:N/A:N
7.5
NVDCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
7.3
secure@microsoft.comCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
7.3
microsoftCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C

Direct CVE/CNA normalized decisions

7.3Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C
Validation
Valid match
Recomputed
7.3
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.