SARA / Free Tools / CVE / CVE-2021-33766

CVE-2021-33766 — Microsoft Exchange Server Information Disclosure

Microsoft Exchange Server Information Disclosure Vulnerability

CVSS

7.3 HIGH

EPSS

93.74% (top 0.20%)

CWE

—

Published

2021-07-14T17:53:40.000Z

Last modified

2025-10-21T23:25:41.207Z

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C

CISA KEV — Actively Exploited

Added to KEV

2022-01-18

BOD 22-01 due

2022-02-01

Ransomware use

Unknown

View KEV detail

01What is this vulnerability?

Microsoft Exchange Server Information Disclosure Vulnerability

Vendor	Product	Versions
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 9	15.02.0
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 20	15.01.0
Microsoft	Microsoft Exchange Server 2013 Cumulative Update 23	15.00.0
Microsoft	Microsoft Exchange Server 2016 Cumulative Update 19	15.01.0
Microsoft	Microsoft Exchange Server 2019 Cumulative Update 8	15.02.0

Yes — actively exploited. Added to the CISA KEV catalog on 2022-01-18. Ransomware use: Unknown.

Patch to a fixed version listed in the vendor advisory (see references below).
Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
Hunt historical logs for exploitation indicators — see Detection signatures below.

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

portal.msrc.microsoft.com — https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-3376…
www.zerodayinitiative.com — https://www.zerodayinitiative.com/advisories/ZDI-21-798/

Want this in your SOAR or SIEM?
SARA's API returns EPSS, CVSS, KEV, and an analyst-grade summary in one call.