# CASCA evidence receipt — CVE-2021-26855

- Generation: `gen-409cbd0c74ff4feb70e4944e6b98ce40`
- As known: 2026-07-21T08:13:17.697275+00:00
- Comparison: gen-56ccdaf914f7b4be95b689ccae7dc20d
- Score policy: public-priority-v1.0.1
- Conflict: present

## Source assertions

- **CISA-ADP** (independent_enrichment): container — CISA ADP Vulnrichment
  - Observed: 2026-07-19T04:27:06.398189+00:00
  - Citation: https://www.cve.org/CVERecord?id=CVE-2021-26855
- **CVE** (derivative_copy): container — CVE Program Container
  - Observed: 2026-07-19T04:27:06.398189+00:00
  - Citation: https://www.cve.org/CVERecord?id=CVE-2021-26855
- **microsoft** (original_assertion): container — Microsoft Exchange Server Remote Code Execution Vulnerability
  - Observed: 2026-07-19T04:27:06.398189+00:00
  - Citation: https://www.cve.org/CVERecord?id=CVE-2021-26855
- **CISA KEV** (original_assertion): observed_exploitation — Microsoft Exchange Server Remote Code Execution Vulnerability
  - Observed: 2026-07-19T04:54:04.25158+00:00
  - Citation: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- **FIRST EPSS** (original_assertion): model_probability — Probability 0.999990000000; percentile 0.999910000000
  - Observed: 2026-07-19T04:54:35.756809+00:00
  - Citation: https://www.first.org/epss/data_stats.html

## CVSS assessments

- **nvd@nist.gov** (Primary, CVSS 2.0): 7.5 — score eligible
  - Evidence class: nvd_enrichment_exact; source rank: 0
  - Validation: valid_match
  - Vector: `AV:N/AC:L/Au:N/C:P/I:P/A:P`
- **nvd@nist.gov** (Secondary, CVSS 3.1): 9.8 — score eligible
  - Evidence class: nvd_enrichment_exact; source rank: 0
  - Validation: valid_match
  - Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- **secure@microsoft.com** (Secondary, CVSS 3.1): 9.1 — score eligible
  - Evidence class: exact_record_cna; source rank: 1
  - Validation: valid_match
  - Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- **microsoft** (unknown, CVSS 3.1): 9.1 — display only
  - Evidence class: direct_cve_record_display_only; source rank: not applicable
  - Validation: display-only direct record assessment
  - Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C`

## Applicability scope

- **Microsoft · Microsoft Exchange Server 2013 Cumulative Update 21** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2013 Cumulative Update 22** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2013 Cumulative Update 23** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.00.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 10** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 11** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 12** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 13** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 14** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 15** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 16** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 17** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 18** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 19** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 8** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2016 Cumulative Update 9** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.01.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 1** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 2** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 3** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 4** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 5** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 6** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 7** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **Microsoft · Microsoft Exchange Server 2019 Cumulative Update 8** (direct_source; unknown)
  - Versions: [{"status": "affected", "version": "15.02.0", "lessThan": "publication", "versionType": "custom"}]
- **microsoft · exchange_server** (vulnerable_target; supported)
  - Versions: Version 2013; Version 2016; Version 2019
  - Canonical identity: `product-d87daca995d075bf30565cc429e7242a47683272975068df1d327ec1d8ff609c`
  - Official link states: linked_exact
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*`
  - Criterion (linked_exact, vulnerable_target): `cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*`

## Identity source boundaries

- **cpe_dictionary**: 1775266 records through 2026-07-21T06:45:29.809553+00:00
  - Run: `27d65b0f-b718-4b4f-bb79-c47c68d09dfa`
- **cpe_match**: 643502 records through 2026-07-21T08:13:17.697275+00:00
  - Run: `955dae73-7302-438b-aee1-058d7cc5d48e`

## Limitations and unknowns

- 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; unresolved scope remains unknown.
- NVD-carried upstream facts remain derivative and are not independent corroboration.
- 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.
- Factor D remains unknown because WC-03 has not converted canonical CPE mappings into generation-bound mapping obligations; canonical identity alone does not score applicability.
- Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.

Generated from CASCA normalized evidence. This receipt is not proof that an asset is affected, unaffected, safe, or fixed.