Which products and versions are affected by CVE-2021-33766?

Affected: Exchange Server (Microsoft) versions 2013-cumulative_update_23, 2016-cumulative_update_19, 2016-cumulative_update_20, 2019-cumulative_update_8, 2019-cumulative_update_9. The full list is in the CVE brief.

Is CVE-2021-33766 being exploited in the wild?

It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Dec 21, 2021.

Is CVE-2021-33766 in the CISA KEV catalog?

Yes. It was added on Jan 18, 2022 with a federal remediation due date of Feb 1, 2022.

Is there a public exploit for CVE-2021-33766?

Public exploit code is available.

Is there a fix for CVE-2021-33766?

Fixed versions are available, including Exchange Server 15.00.1497.015, Exchange Server 15.01.2176.012, Exchange Server 15.01.2242.008.

How urgently should CVE-2021-33766 be patched?

Brandefense priority: patch immediately, because it is listed as exploited in the wild.

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Vulnerability Intelligence

CVE-2021-33766

HighExploitedPublic exploit

Microsoft Exchange Server Information Disclosure Vulnerability

Published Jul 14, 2021 · Updated Aug 10, 2026

Key Facts

Patch immediately

CVE-2021-33766 is a high-severity vulnerability (CVSS 7.5 v3.1) affecting Exchange Server (Microsoft).
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Dec 21, 2021. Public exploit code is available.
EPSS estimates a 98% probability of exploitation in the next 30 days.
Fixed versions are available, including Exchange Server 15.00.1497.015, Exchange Server 15.01.2176.012, Exchange Server 15.01.2242.008.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.

CVSS v3.1

7.5

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

EPSS (30-day exploit likelihood)

98%

Higher than 99.9% of all scored CVEs

Exploited in the wild

Yes

4 catalog listings

Public exploit code

Available

Proof-of-concept or weaponized module

Get the full CVE-2021-33766 brief as a PDF

Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.

Description

Microsoft Exchange Server Information Disclosure Vulnerability

Known-Exploited Catalog Listings

Catalog	Added	Remediation due	Ransomware use
CISA KEV	Jan 18, 2022	Feb 1, 2022	Not reported
Industry KEV feed	Dec 21, 2021	Feb 1, 2022	Not reported
CIRCL KEV	Jan 18, 2022	Feb 1, 2022	Not reported
ENISA EUVD	Jan 18, 2022	n/a	Not reported

Required action: Apply updates per vendor instructions.

Affected Products

5 affected entries in total

Product	Affected versions	Fixed in
Exchange ServerMicrosoft	2013-cumulative_update_23, 2016-cumulative_update_19, 2016-cumulative_update_20, 2019-cumulative_update_8, 2019-cumulative_update_9	15.00.1497.015

Patched Releases

Exchange Server

15.00.1497.015, 15.01.2176.012, 15.01.2242.008, 15.02.0792.013, 15.02.0858.010

Timeline

Publicly disclosed
Jul 14, 2021
Added to Industry KEV feed
Dec 21, 2021
Added to CISA KEV
Jan 18, 2022
Added to CIRCL KEV
Jan 18, 2022
Added to ENISA EUVD
Jan 18, 2022
Last updated
Aug 10, 2026

References

4 more references in the full CVE brief

FAQ

Common Questions.

Microsoft Exchange Server Information Disclosure Vulnerability
Affected: Exchange Server (Microsoft) versions 2013-cumulative_update_23, 2016-cumulative_update_19, 2016-cumulative_update_20, 2019-cumulative_update_8, 2019-cumulative_update_9. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Dec 21, 2021.
Yes. It was added on Jan 18, 2022 with a federal remediation due date of Feb 1, 2022.
Public exploit code is available.
Fixed versions are available, including Exchange Server 15.00.1497.015, Exchange Server 15.01.2176.012, Exchange Server 15.01.2242.008.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.

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