CASCACascade Atlas

Evidence dossier

CVE-2026-21509

Microsoft Office Security Feature Bypass Vulnerability

Exploited in the wild (CISA KEV since Jan 26, 2026). microsoft reports CVSS 3.1 7.8. EPSS estimates 72.6% exploit likelihood as of Aug 26, 2026.

80.7–84.5Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

State
PUBLISHED
Published
Jan 26, 2026
Updated
Jul 30, 2026
Evidence coverage
95%

Evidence chronology

What was known when

Download this view's receipt →
  1. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Microsoft Office Security Feature Bypass Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Microsoft Office Security Feature Bypass Vulnerability
    Original evidence ↗
  2. 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 ↗
  3. 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 ↗
  4. Source dateSource date omittedFirst observed by CASCA
    microsoft

    Record text: Microsoft Office Security Feature Bypass Vulnerability

    Inspect raw assertion
    Field
    container
    Value
    Microsoft Office Security Feature Bypass Vulnerability
    Original evidence ↗
  5. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 72.55% probability · 99.4th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.725540000000; percentile 0.993960000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Jan 26, 2026 · first observed Jul 19, 2026

Exploit likelihood72.55%

FIRST EPSS · score date Aug 26, 2026 · 99.4th percentile · first observed Aug 26, 2026

SeverityCVSS 7.8

microsoft · CVSS 3.1 · first observed Aug 1, 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 KEVOriginal assertion
Exploitation cataloged

Microsoft Office Security Feature Bypass Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Microsoft Office Security Feature Bypass Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
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 Office Security Feature Bypass Vulnerability

Inspect raw assertion
Field
container
Value
Microsoft Office Security Feature Bypass Vulnerability
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

72.55% probability · 99.4th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.725540000000; percentile 0.993960000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
10Underlying assertions
3Canonical products
10Target 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

8 scope groups

microsoft · source assertedMicrosoftMicrosoft 365 Apps for EnterpriseDirect source scope
Affected: 16.0.1 to before https://aka.ms/OfficeSecurityReleases (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "16.0.1", "lessThan": "https://aka.ms/OfficeSecurityReleases", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Office 2016Direct source scope
Affected: 16.0.0 to before 16.0.5539.1001 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "16.0.0", "lessThan": "16.0.5539.1001", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Office 2019Direct source scope
Affected: 19.0.0 to before 16.0.10417.20095 (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "19.0.0", "lessThan": "16.0.10417.20095", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Office LTSC 2021Direct source scope
Affected: 16.0.1 to before https://aka.ms/OfficeSecurityReleases (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "16.0.1", "lessThan": "https://aka.ms/OfficeSecurityReleases", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft Office LTSC 2024Direct source scope
Affected: 16.0.0 to before https://aka.ms/OfficeSecurityReleases (custom comparison)
Source-reported scope

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

Inspect raw assertion[{"status": "affected", "version": "16.0.0", "lessThan": "https://aka.ms/OfficeSecurityReleases", "versionType": "custom"}]
NVD CPE · APPLICATIONmicrosoft365_appsVulnerable target · 2 assertions
Version not applicableCanonical identity product-14a59f3c1c4fc4cec4da9e1d602ac339da114e67c884352e121c41fb03b7a712Linked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    3259ebfe-ae2d-48b8-be9a-e22bbdb31378
  2. cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    cd25f492-9272-4836-832c-8439ebe64ccf
NVD CPE · APPLICATIONmicrosoftofficeVulnerable target · 4 assertions
Version 2016; Version 2019Canonical identity product-f4efee17050cd92d62299077c43827052b373ddcb783c02caa43c2fbb378d2f4Linked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 4
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    cf5ddd09-902e-4881-98d0-cb896333b4aa
  2. cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 5
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    26a3b226-5d7c-4556-9350-5222dc8efc2c
  3. cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x64:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 2
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    72324216-4eb3-4243-a007-fef3133c7df9
  4. cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x86:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 3
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    0fbb0e61-7997-4f26-9c07-54912d3f1c10
NVD CPE · APPLICATIONmicrosoftoffice_long_term_servicing_channelVulnerable target · 4 assertions
Version 2021; Version 2024Canonical identity product-911e466d0be7cb2953297756c47cb44a2f472c517f89b133f4ff5b03a0ab5264Linked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 8
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    d31e509a-0b2e-4b41-88c4-0099e800afe6
  2. cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x64:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 6
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    851bac4e-9965-4f40-9a6c-b73d9004f4c1
  3. cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 9
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    017a7041-bef1-4e4e-ac8a-efc6afeb01fe
  4. cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 7
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    23b2fa23-76f4-4d83-a718-b8d04d7ea37b

Affected-product evidence

Accepted scope and product mapping

3 canonical links · 1 source-reported links

Mapping establishedEvidence supported

vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-14a59f3c1c4fc4cec4da9e1d602ac339da114e67c884352e121c41fb03b7a712

Source class
Nvd cpe vulnerable target
Assertions
2
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
14052db9-b3c4-45f4-b0fa-a3029cde4bcb572a602a-afe4-4744-b58e-6c8794a5e586
Mapping establishedEvidence supported

vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-911e466d0be7cb2953297756c47cb44a2f472c517f89b133f4ff5b03a0ab5264

Source class
Nvd cpe vulnerable target
Assertions
4
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
17c4b441-4796-4579-adea-5ea2227d49af1f706b8c-a571-4a65-bf37-4dd895eb52e69a9f28aa-41f8-4c86-be1c-9bb37890cf4fca45fc22-9d15-4635-99eb-9752fb39bf98
Mapping establishedEvidence supported

vendor-01299a5a765aea70faa05f2d06e0c26a5d498fd34553e868d89e8a43b31864db · product-f4efee17050cd92d62299077c43827052b373ddcb783c02caa43c2fbb378d2f4

Source class
Nvd cpe vulnerable target
Assertions
4
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
8ff819bc-2411-4ed6-aca0-e7587befcb879e9f3995-eced-47fc-a2b4-f38a29e42f04d9b80884-b37f-40c4-b1d4-f8928ce5b941f09ac323-6b93-4c8d-8a66-0a0b37be4c16
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
Aug 27, 2026
Retained assertion IDs
1e7e1280-4574-4a69-bcde-6e64a55e0bd6b247861d-4828-4022-acee-c227979b69f6b5b772f2-437a-4a87-aa05-be550d5026f2dc5d5b24-2c87-4f13-a017-82835f47ec74e7e84a2b-7849-46aa-b734-a56295ed8581

Assessments

CVSS by origin

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.