CVE-2021-26858

Exploitation

Exploited in the wild. Listed in the CISA Known Exploited Vulnerabilities catalog on 2021-11-03. Federal remediation due 2022-05-03. Known ransomware campaign use: reported by CISA.

SSVC decision

• ExploitationactiveCISA reports credible evidence of active exploitation.
• AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
• Technical ImpacttotalSuccessful exploitation gives total control of the vulnerable component.

CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.

EPSS probability

93.65% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 99.8% of scored records. A rank, not a probability.

NVD base score

7.8 (CVSS v3.x), scored by the NVD independently of the CNA.

NVD CVSS vector

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

NVD analysis status

Analyzed. NVD last modified this record on 2026-10-01.

Red Hat severity

No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2021-03-02 23:55Z5 YR AGO

Last updated

2026-10-01 20:12Z28 DAYS AGO

Reserved

2021-02-08

Assigning CNA

microsoft

Record state

PUBLISHED

Severity

High (CVSS 7.8)

CNA CVSS vector

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

Weaknesses

No CWE assigned

Data version

5.2

Document digest

cbfe620d680d8784b6855a5029c6a28028e4df0ad119267c052c4a5a78b70c8c

• msrc.microsoft.comMicrosoft Exchange Server Remote Code Execution Vulnerabilityhttps://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26858vendor-advisorypatch
• portal.msrc.microsoft.comhttps://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858x_refsource_MISC
• www.cisa.govhttps://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858government-resource