CVE-2021-26857
HighExploitedPublic exploitMicrosoft Exchange Server Remote Code Execution Vulnerability
Published Sep 14, 2022 · Updated Aug 19, 2026
Key Facts
Patch immediately- CVE-2021-26857 is a high-severity vulnerability (CVSS 7.8 v3.1) affecting Exchange Server (Microsoft), Microsoft Exchange Server 2010 Service Pack 3, Microsoft Exchange Server 2013 Cumulative Update 21 and 22 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Mar 2, 2021 and is known to be used in ransomware campaigns. Public exploit code is available.
- EPSS estimates a 96% probability of exploitation in the next 30 days.
- Fixed versions are available, including Exchange Server 14.03.0513.000, Exchange Server 15.00.0847.064, Exchange Server 15.00.1395.012.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
7.8
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
96%
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-2021-26857 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 3, 2021 | May 3, 2022 | Known |
| Industry KEV feed | Mar 2, 2021 | May 3, 2022 | Known |
| CIRCL KEV | Nov 3, 2021 | May 3, 2022 | Known |
| ENISA EUVD | Nov 3, 2021 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
78 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Exchange ServerMicrosoft | 2010-sp3, 2013-cumulative_update_1, 2013-cumulative_update_21, 2013-cumulative_update_22, 2013-cumulative_update_23, 2013-sp1, 2016-cumulative_update_10, 2016-cumulative_update_11 | 15.02.0221.018 |
| Microsoft Exchange Server 2010 Service Pack 3 | >= 14.0.0.0 | 14.03.0513.000 |
| Microsoft Exchange Server 2013 Cumulative Update 21 | >= 15.00.0 | 15.00.1395.012 |
| Microsoft Exchange Server 2013 Cumulative Update 22 | >= 15.00.0 | 15.00.1473.006 |
| Microsoft Exchange Server 2013 Cumulative Update 23 | >= 15.00.0 | 15.00.1497.012 |
Patched Releases
Exchange Server
14.03.0513.000, 15.00.0847.064, 15.00.1395.012, 15.00.1473.006, 15.00.1497.012, 15.01.1415.010, 15.01.1466.016, 15.01.1531.012, 15.01.1591.018, 15.01.1713.010, 15.01.1779.008, 15.01.1847.012, 15.01.1913.012, 15.01.1979.006, 15.01.1979.008, 15.01.2044.013, 15.01.2106.013, 15.01.2176.009, 15.02.0221.018, 15.02.0397.011, 15.02.0464.015, 15.02.0529.013, 15.02.0595.008, 15.02.0659.012, 15.02.0721.013, 15.02.0792.010, publication
Microsoft Exchange Server 2010 Service Pack 3
14.03.0513.000
Microsoft Exchange Server 2013 Cumulative Update 21
15.00.1395.012
Microsoft Exchange Server 2013 Cumulative Update 22
15.00.1473.006
Microsoft Exchange Server 2013 Cumulative Update 23
15.00.1497.012
Microsoft Exchange Server 2013 Service Pack 1
15.00.0847.064
Microsoft Exchange Server 2016 Cumulative Update 10
15.01.1531.012
Microsoft Exchange Server 2016 Cumulative Update 11
15.01.1591.018
Microsoft Exchange Server 2016 Cumulative Update 12
15.01.1713.010
Microsoft Exchange Server 2016 Cumulative Update 13
15.01.1779.008
Microsoft Exchange Server 2016 Cumulative Update 14
15.01.1847.012
Microsoft Exchange Server 2016 Cumulative Update 15
15.01.1913.012
Microsoft Exchange Server 2016 Cumulative Update 16
15.01.1979.008
Microsoft Exchange Server 2016 Cumulative Update 17
15.01.2044.013
Microsoft Exchange Server 2016 Cumulative Update 18
15.01.2106.013
Microsoft Exchange Server 2016 Cumulative Update 19
15.01.2176.009
Microsoft Exchange Server 2016 Cumulative Update 8
15.01.1415.010
Microsoft Exchange Server 2016 Cumulative Update 9
15.01.1466.016
Microsoft Exchange Server 2019
15.02.0221.018
Microsoft Exchange Server 2019 Cumulative Update 1
15.01.1979.006
Microsoft Exchange Server 2019 Cumulative Update 2
15.02.0397.011
Microsoft Exchange Server 2019 Cumulative Update 3
15.02.0464.015
Microsoft Exchange Server 2019 Cumulative Update 4
15.02.0659.012
Microsoft Exchange Server 2019 Cumulative Update 5
15.02.0595.008
Microsoft Exchange Server 2019 Cumulative Update 6
15.02.0529.013
Timeline
Added to Industry KEV feed
Mar 2, 2021
Added to CISA KEV
Nov 3, 2021
Added to CIRCL KEV
Nov 3, 2021
Added to ENISA EUVD
Nov 3, 2021
Publicly disclosed
Sep 14, 2022
Last updated
Aug 19, 2026
Weakness Type
- CWE-502 Deserialization of Untrusted Data
References
- advisoryhttp://feedproxy.google.com/~r/TheHackersNews/~3/YNZgPucSGkw/icrosoft-exchange-ransomware.html
- advisoryhttps://blogs.microsoft.com/on-the-issues/2021/03/02/new-nation-state-cyberattacks/
- advisoryhttps://docs.microsoft.com/en-us/lifecycle/products/exchange-server-2010
- advisoryhttps://fidelissecurity.com/threatgeek/threat-intelligence/microsoft-exchange-vulnerabilities/Microsoft-Exchange-Vulnerabilities
- advisoryhttps://github.com/microsoft/CSS-Exchange/tree/main/Security
FAQ
Common Questions.
Microsoft Exchange Server Remote Code Execution Vulnerability
Affected: Exchange Server (Microsoft) versions 2010-sp3, 2013-cumulative_update_1, 2013-cumulative_update_21, 2013-cumulative_update_22, 2013-cumulative_update_23, 2013-sp1, 2016-cumulative_update_10, 2016-cumulative_update_11; Microsoft Exchange Server 2010 Service Pack 3 versions >= 14.0.0.0; Microsoft Exchange Server 2013 Cumulative Update 21 versions >= 15.00.0, 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 Mar 2, 2021 and is known to be used in ransomware campaigns.
Yes. It was added on Nov 3, 2021 with a federal remediation due date of May 3, 2022.
Public exploit code is available.
Fixed versions are available, including Exchange Server 14.03.0513.000, Exchange Server 15.00.0847.064, Exchange Server 15.00.1395.012.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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