CVE
CVE-2021-26855
- First Reported
- Apr 30, 2026
- Latest Reported
- Sep 3, 2026
CVE Enrichment
- CVSS
- 9.1 CRITICAL
- EPSS
- 100.00%
- EPSS Percentile
- 99.99%
- CISA KEV
- YES — Known Exploited Vulnerability
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Technical Details
- CVSS Version
- 3.1
- CNA / NVD Source
- secure@microsoft.com
- Published
- 03-Mar-2021 07:15
- Last Modified
- 20-Aug-2026 02:22
- EPSS Date
- 2026-10-12
- CWE
- CWE-918
CVSS Vector
CVSS:3.1 AV:N /
AC:L /
PR:N /
UI:N /
S:U /
C:H /
I:H /
A:N
CISA KEV Details
- Date Added
- 2021-11-03
- Remediation Due
- 2022-05-03
- Known Ransomware Campaign Use
- Known
- Required Action
- Apply updates per vendor instructions.
- Notes
- Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26855
Affected Products / Versions
- microsoft / exchange_server
Version / affected range: 2013
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2013
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2013
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2016
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:* - microsoft / exchange_server
Version / affected range: 2019
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
References
- secure@microsoft.com
- af854a3a-2127-422b-91ae-364da2661108
- af854a3a-2127-422b-91ae-364da2661108
- af854a3a-2127-422b-91ae-364da2661108
- af854a3a-2127-422b-91ae-364da2661108
- af854a3a-2127-422b-91ae-364da2661108
- CISA Advisory
Last enrichment sync: 12-Oct-2026 23:15
Sources: NVD · FIRST EPSS · CISA KEV
Latest successful provider update; providers refresh independently.
Sources: NVD · FIRST EPSS · CISA KEV
Latest successful provider update; providers refresh independently.
Reported Context (3)
- Separately, Mimikatz was also associated with the China-linked SHADOW-EARTH-053’s exploitation of CVE-2021-26855, which affected Microsoft Exchange Server. Recorded Future Reports 215 Actively Exploited CVEs and Expanding Supply-Chain Threats in H1 2026
- CVE-2021-26855 Recorded Future Reported 59 High-Impact Vulnerabilities in June, 56 Actively Exploited
- We have observed them targeting server-based N-day vulnerabilities, such as the ProxyLogon chain targeting Microsoft Exchange Server (CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065). China-Aligned SHADOW-EARTH-053 Targets Asian Government and Critical Infrastructure
CVE (62)
Malware (62)
People (2)
Threat Actors (23)
MITRE ATT&CK (28)
Vendors (44)
Products (107)
Tools (24)
Industries (16)
Countries (17)
Note: Related entities, including threat actors, malware, CVEs, MITRE ATT&CK techniques, vendors, products, tools, countries, and industries, are shown when they appear in the same reporting. Their presence does not necessarily mean they were targeted, compromised, vulnerable, responsible for the activity, or directly involved in the incident.