CVE-2021-42321
HighExploitedPublic exploitMicrosoft Exchange Server Remote Code Execution Vulnerability
Published Mar 2, 2022 · Updated Aug 19, 2026 · Also known as TR-21-0903, TR-22-0188
Key Facts
Patch immediately- CVE-2021-42321 is a high-severity vulnerability (CVSS 8.8 v3.1) affecting Exchange Server (Microsoft), Microsoft Exchange Server 2016 Cumulative Update 21, Microsoft Exchange Server 2016 Cumulative Update 22 and 2 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Nov 9, 2021 and is known to be used in ransomware campaigns. Public exploit code is available.
- EPSS estimates a 92% probability of exploitation in the next 30 days.
- Fixed versions are available, including Exchange Server 15.01.2308.020, Exchange Server 15.01.2375.017, Exchange Server 15.02.0792.019.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
8.8
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
92%
Higher than 99.8% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings, used by ransomware
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-42321 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 Remote Code Execution Vulnerability
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Nov 17, 2021 | Dec 1, 2021 | Known |
| Industry KEV feed | Nov 9, 2021 | Dec 1, 2021 | Known |
| CIRCL KEV | Nov 17, 2021 | Dec 1, 2021 | Known |
| ENISA EUVD | Nov 17, 2021 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
12 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Exchange ServerMicrosoft | 2016-cumulative_update_21, 2016-cumulative_update_22, 2019-cumulative_update_10, 2019-cumulative_update_11 | 15.01.2308.020 |
| Microsoft Exchange Server 2016 Cumulative Update 21 | >= 15.01.0 | 15.01.2308.020 |
| Microsoft Exchange Server 2016 Cumulative Update 22 | >= 15.0.0 | 15.01.2375.017 |
| Microsoft Exchange Server 2019 Cumulative Update 10 | >= 15.02.0 | 15.02.0792.019 |
| Microsoft Exchange Server 2019 Cumulative Update 11 | >= 15.02.0 | 15.02.0986.014 |
Patched Releases
Exchange Server
15.01.2308.020, 15.01.2375.017, 15.02.0792.019, 15.02.0986.014
Microsoft Exchange Server 2016 Cumulative Update 21
15.01.2308.020
Microsoft Exchange Server 2016 Cumulative Update 22
15.01.2375.017
Microsoft Exchange Server 2019 Cumulative Update 10
15.02.0792.019
Microsoft Exchange Server 2019 Cumulative Update 11
15.02.0986.014
Timeline
Added to Industry KEV feed
Nov 9, 2021
Added to CISA KEV
Nov 17, 2021
Added to CIRCL KEV
Nov 17, 2021
Added to ENISA EUVD
Nov 17, 2021
Publicly disclosed
Mar 2, 2022
Last updated
Aug 19, 2026
References
- advisoryhttp://feedproxy.google.com/
- advisoryhttps://admin.usom.gov.tr/web-security/ssrf
- advisoryhttps://blog.talosintelligence.com/2021/11/microsoft-patch-tuesday-for-nov-2021.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+feedburner/Talos+(Talos%E2%84%A2+Blog)Microsoft
- advisoryhttps://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-21980
- advisoryhttps://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-22049
FAQ
Common Questions.
Microsoft Exchange Server Remote Code Execution Vulnerability
Affected: Exchange Server (Microsoft) versions 2016-cumulative_update_21, 2016-cumulative_update_22, 2019-cumulative_update_10, 2019-cumulative_update_11; Microsoft Exchange Server 2016 Cumulative Update 21 versions >= 15.01.0; Microsoft Exchange Server 2016 Cumulative Update 22 versions >= 15.0.0, among others. 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 Nov 9, 2021 and is known to be used in ransomware campaigns.
Yes. It was added on Nov 17, 2021 with a federal remediation due date of Dec 1, 2021.
Public exploit code is available.
Fixed versions are available, including Exchange Server 15.01.2308.020, Exchange Server 15.01.2375.017, Exchange Server 15.02.0792.019.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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