CVE-2021-26858

CVE Enrichment

CVSS: 7.8 HIGH
EPSS: 93.65%
EPSS Percentile: 99.84%
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: 02-Oct-2026 04:17
EPSS Date: 2026-10-12

CVSS Vector


            CVSS:3.1                            AV:L /
                            AC:L /
                            PR:N /
                            UI:R /
                            S:U /
                            C:H /
                            I:H /
                            A:H

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-2021-26858

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

Last enrichment sync: 13-Oct-2026 06:09
Sources: NVD · FIRST EPSS · CISA KEV
Latest successful provider update; providers refresh independently.

Reported Context (1)

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 (4)

Malware (8)

People (2)

Threat Actors (6)

MITRE ATT&CK (17)

Vendors (1)

Products (5)

Tools (12)

Industries (7)

Countries (9)

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.