CASCACascade Atlas

Evidence dossier

CVE-2021-27085

Internet Explorer Remote Code Execution Vulnerability

Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 8.8. EPSS estimates 5.4% exploit likelihood as of Aug 27, 2026.

69.3–70.9Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

Internet Explorer Remote Code Execution Vulnerability

State
PUBLISHED
Published
Mar 11, 2021
Updated
Oct 21, 2025
Evidence coverage
92%

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: Internet Explorer Remote Code Execution Vulnerability

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

    Exploitation cataloged: Microsoft Internet Explorer Remote Code Execution Vulnerability

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

    EPSS score: 5.45% probability · 92.15th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.054480000000; percentile 0.921460000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Nov 3, 2021 · first observed Jul 19, 2026

Exploit likelihood5.45%

FIRST EPSS · score date Aug 27, 2026 · 92.1th percentile · first observed Aug 27, 2026

SeverityCVSS 8.8

microsoft · CVSS 3.1 · first observed Jul 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 statusEvidence supported

Eligible evidence is present for this bounded claim.

Revision
evidence-policy-v1.1.0
Cutoff
Aug 27, 2026
Resolution
None
Exploit likelihoodEvidence supported

Eligible evidence is present for this bounded claim.

Revision
evidence-policy-v1.1.0
Cutoff
Aug 27, 2026
Resolution
None
Severity assessmentEvidence supported

Eligible evidence is present for this bounded claim.

Revision
casca-direct-cvss-eligibility-v1
Cutoff
Aug 27, 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
Aug 27, 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

Internet Explorer Remote Code Execution Vulnerability

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

Microsoft Internet Explorer Remote Code Execution Vulnerability

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

5.45% probability · 92.15th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.054480000000; percentile 0.921460000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
7Underlying assertions
7Canonical products
1Target assertions
6Constraint assertions

Grouped from 2 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

8 scope groups

microsoft · source assertedMicrosoftInternet Explorer 11Direct source scope
Affected: 1.0.0 to before publication (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "1.0.0", "lessThan": "publication", "versionType": "custom"}]
NVD CPE · APPLICATIONmicrosoftinternet_explorerVulnerable target · 1 assertions
Version 11Canonical identity product-d26e3505f2452daa926474c7ca23fc78f73a7b20902783174428ff8d6e276baaLinked exact
Scope supported
Inspect raw assertion
  1. cpe:2.3:a:microsoft:internet_explorer:11:-:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    d7809f78-8d56-4925-a8f9-4119b973a667
NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1803Environmental constraint · 1 assertions
Version not applicableCanonical identity product-5e821ea3746af154a469c180e78b9f4d663edf21461517987eed76740c7910c1Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_10_1803:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    00345596-e9e0-4096-8dc6-0212f4747a13
NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1809Environmental constraint · 1 assertions
Version not applicableCanonical identity product-a3084138383423221f61594e86f5b295e5e254acd7ae5284f45e0877a084db43Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_10_1809:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 1
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    2e332666-2e03-468e-bc30-299816d6e8ed
NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_1909Environmental constraint · 1 assertions
Version not applicableCanonical identity product-ef5324dcc791e4e872d6c2be0aefa1d7687ca82c3b4ac5d1f72c76cce8395218Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_10_1909:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 2
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    a1b570a8-ed1a-46b6-b8ab-064445f8fc4c
NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_2004Environmental constraint · 1 assertions
Version not applicableCanonical identity product-9b245936275be71b526838fc72ea633d195b35bdd9dfc31bb6df51e7700edeccLinked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_10_2004:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 3
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    d4dbe5b2-ae10-4251-bcda-dc5edee6ee67
NVD CPE · OPERATING SYSTEMmicrosoftwindows_10_20h2Environmental constraint · 1 assertions
Version not applicableCanonical identity product-55e90faed8848f3d316cf702d119e83086b6dc5a963d9947a7df1c589f50346dLinked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_10_20h2:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 4
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    6afd13a6-a390-4400-9029-2f4058ca17e2
NVD CPE · OPERATING SYSTEMmicrosoftwindows_server_2019Environmental constraint · 1 assertions
Version not applicableCanonical identity product-25a2932c0bbcb648f7e391c8b9d34c734e5085444c03c1c206b9d4c4baa80b25Linked exact
Scope constrained
Inspect raw assertion
  1. cpe:2.3:o:microsoft:windows_server_2019:-:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Environmental constraint
    Configuration
    0 · node/1 · match 5
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    db79ee26-fc32-417d-a49c-a1a63165a968

Affected-product evidence

Accepted scope and product mapping

1 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-d26e3505f2452daa926474c7ca23fc78f73a7b20902783174428ff8d6e276baa

Source class
Nvd cpe vulnerable target
Assertions
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
3139949b-adbb-4420-9dde-6a62bae0b5a2
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
1
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
efdfa9c0-4f75-4c74-be13-08199701dd0c

Assessments

CVSS by origin

7.6
NVDCVSS 2.0 · role Primary · priority eligiblevalid_matchAV:N/AC:H/Au:N/C:C/I:C/A:C
8.8
NVDCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8
secure@microsoft.comCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
8.8
microsoftCVSS 3.1 · role unknown · display onlyDirect record assessment retained outside normalized eligibilityCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

Direct CVE/CNA normalized decisions

8.8Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C
Validation
Valid match
Recomputed
8.8
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.