CISA KEV · Known exploitedHigh

CVE-2021-33766

Microsoft Exchange Server

CVE-2021-33766 affects Microsoft Exchange Server. Review the CVSS score, exploitation signals, affected versions, remediation status, and linked source material before making a change.

CVSS
7.5
EPSS
97.5%
99.9% percentile
CISA KEV
Listed
Published
2021.07.15
PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV
Exploit probability97.5%
Technical severityCVSS 7.5

Vulnerability overview

CVE-2021-33766 affects Microsoft Exchange Server. Review the CVSS score, exploitation signals, affected versions, remediation status, and linked source material before making a change.

Affected product and versions

Product
Microsoft Exchange Server
Affected versions
15.02.0, 15.01.0, 15.00.0, 2013, 2016, 2019
Fixed versions
No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
CISA required action

Apply updates per vendor instructions.

Due date: 2022.02.01
  1. 1
    Identify

    Confirm that Microsoft Exchange Server and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CWE
CWE-287
KEV added
2022.01.18
Ransomware use
미확인