CASCACascade Atlas

Evidence dossier

CVE-2026-55040

Microsoft SharePoint Server Security Feature Bypass Vulnerability

Exploited in the wild (CISA KEV since Aug 18, 2026). microsoft reports CVSS 3.1 9.1. EPSS estimates 39.7% exploit likelihood as of Aug 27, 2026.

75.3–82.8Priority evidence range
Evidence current through Aug 27, 2026, 6:09 PM UTC

As of Aug 27, 2026

Normalized restatement

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

State
PUBLISHED
Published
Jul 14, 2026
Updated
Aug 3, 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
    microsoft

    Record text: Microsoft SharePoint Server Security Feature Bypass Vulnerability

    Inspect raw assertion
    Field
    container
    Value
    Microsoft SharePoint Server Security Feature Bypass Vulnerability
    Original evidence ↗
  3. Source dateFirst observed by CASCA
    CISA KEV

    Exploitation cataloged: Microsoft SharePoint Weak Authentication Vulnerability

    Inspect raw assertion
    Field
    observed_exploitation
    Value
    Microsoft SharePoint Weak Authentication Vulnerability
    Original evidence ↗
  4. Source dateFirst observed by CASCA
    FIRST EPSS

    EPSS score: 39.65% probability · 98.51th percentile

    Inspect raw assertion
    Field
    model_probability
    Value
    Probability 0.396520000000; percentile 0.985090000000
    Original evidence ↗
ExploitationCatalog member

CISA KEV · catalog date Aug 18, 2026 · first observed Aug 18, 2026

Exploit likelihood39.65%

FIRST EPSS · score date Aug 27, 2026 · 98.5th percentile · first observed Aug 27, 2026

SeverityCVSS 9.1

microsoft · CVSS 3.1 · first observed Aug 4, 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 ↗
microsoftOriginal assertion
Record text

Microsoft SharePoint Server Security Feature Bypass Vulnerability

Inspect raw assertion
Field
container
Value
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Source dateSource date omittedFirst observed by CASCAOriginal evidence ↗
CISA KEVOriginal assertion
Exploitation cataloged

Microsoft SharePoint Weak Authentication Vulnerability

Inspect raw assertion
Field
observed_exploitation
Value
Microsoft SharePoint Weak Authentication Vulnerability
Source dateFirst observed by CASCAOriginal evidence ↗
FIRST EPSSOriginal assertion
EPSS score

39.65% probability · 98.51th percentile

Inspect raw assertion
Field
model_probability
Value
Probability 0.396520000000; percentile 0.985090000000
Source dateFirst observed by CASCAOriginal evidence ↗

Applicability

Cited product scope

Trace impact →
3Underlying assertions
1Canonical products
3Target 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

4 scope groups

microsoft · source assertedMicrosoftMicrosoft SharePoint Enterprise Server 2016Direct source scope
Affected: 16.0.0 to before 16.0.5561.1001 (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": "16.0.5561.1001", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft SharePoint Server 2019Direct source scope
Affected: 16.0.0 to before 16.0.10417.20175 (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": "16.0.10417.20175", "versionType": "custom"}]
microsoft · source assertedMicrosoftMicrosoft SharePoint Server Subscription EditionDirect source scope
Affected: 16.0.0 to before 16.0.19725.20434 (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": "16.0.19725.20434", "versionType": "custom"}]
NVD CPE · APPLICATIONmicrosoftsharepoint_serverVulnerable target · 3 assertions
Any version (unconstrained) (< 16.0.19725.20434); Version 2016; Version 2019Canonical identity product-77f9def9702aa8ece74aa62c4de32bc72b167cb6f10f2eff44492cf46afc2e03Linked exact
Scope supported
Inspect raw assertions
  1. cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 1
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    f815ef1d-7b60-47be-9ac2-2548f99f10e4
  2. cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 2
    Logic
    OR
    Version bounds
    No explicit bounds
    Match ID
    6122d014-5bf1-4af4-8b4d-80205ed7785e
  3. cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*
    Official link
    Linked exact
    Role
    Vulnerable target
    Configuration
    0 · node/0 · match 0
    Logic
    OR
    Version bounds
    through excluding 16.0.19725.20434
    Match ID
    5fa63ea8-b225-4e35-a6a3-dbdecf5ac4c8

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
3
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
4244f4fa-a69d-4844-9756-a083373cc1b04f142547-a1e3-415f-95e2-8beef8cf64716289f1b5-1bab-48cd-a78f-d6e8b323bba9
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
3
Mapping revision
cpe23-exact-mapping-v1
Observed cutoff
Aug 27, 2026
Retained assertion IDs
14dbf42a-9cf2-41d1-b2e1-eb5494eed9497a3c1e77-7f6f-458c-93c9-0ef72d3aff46a9a94ba4-7bef-419d-bb0d-478a691b8d8f

Assessments

CVSS by origin

9.1
secure@microsoft.comCVSS 3.1 · role Secondary · priority eligiblevalid_matchCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
9.1
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:H/I:H/A:N/E:U/RL:O/RC:C

Direct CVE/CNA normalized decisions

9.1Priority eligible

microsoft

CVSS 3.1 · Primary · Original assertion · rank 1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
Validation
Valid match
Recomputed
9.1
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.