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URL: https://nvd.nist.gov/vuln/detail/CVE-2021-26855

⇱ NVD - CVE-2021-26855

  1. Vulnerabilities

CVE-2021-26855 Detail

Description

Microsoft Exchange Server Remote Code Execution Vulnerability


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NVD assessment not yet provided.

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html CVE, Microsoft Corporation Exploit  Third Party Advisory  VDB Entry 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html CVE, Microsoft Corporation Exploit  Third Party Advisory  VDB Entry 
http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html CVE, Microsoft Corporation Exploit  Third Party Advisory  VDB Entry 
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html CVE, Microsoft Corporation Exploit  Third Party Advisory  VDB Entry 
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855 CVE, Microsoft Corporation Patch  Vendor Advisory 
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855 CISA-ADP US Government Resource 

This CVE is in CISA's Known Exploited Vulnerabilities Catalog

Reference CISA's BOD 22-01 and Known Exploited Vulnerabilities Catalog for further guidance and requirements.

Vulnerability Name Date Added Due Date Required Action
Microsoft Exchange Server Remote Code Execution Vulnerability 11/03/2021 05/03/2022 Apply updates per vendor instructions.

Weakness Enumeration

CWE-ID CWE Name Source
CWE-918 Server-Side Request Forgery (SSRF) 👁 cwe source acceptance level
NIST   CISA-ADP  

Known Affected Software Configurations Switch to CPE 2.2

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Denotes Vulnerable Software
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Change History

22 change records found show changes

CVE Modified by CISA-ADP 6/16/2026 11:43:51 PM

Action Type Old Value New Value
Added SSVC 
{"timestamp":"2024-01-02T18:10:15.970217Z","id":"CVE-2021-26855","options":[{"exploitation":"active"},{"automatable":"yes"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}

CVE Modified by Microsoft Corporation 6/16/2026 11:43:51 PM

Action Type Old Value New Value
Added Affected Record truncated, showing 2048 of 7357 characters.
View Entire Change Record
[{"vendor":"Microsoft","product":"Microsoft Exchange Server 2016 Cumulative Update 19","cpes":["cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.01.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2019 Cumulative Update 8","cpes":["cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.02.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2019","cpes":["cpe:2.3:a:microsoft:exchange_server:2019:*:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.02.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2013 Cumulative Update 22","cpes":["cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.00.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2019 Cumulative Update 2","cpes":["cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.02.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2016 Cumulative Update 13","cpes":["cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.01.0","lessThan":"publication","versionType":"custom","status":"affected"}]},{"vendor":"Microsoft","product":"Microsoft Exchange Server 2013 Cumulative Update 23","cpes":["cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*"],"platforms":["x64-based Systems"],"versions":[{"version":"15.00.0"

CVE CISA KEV Update by Cybersecurity and Infrastructure Security Agency (CISA) U.S. Civilian Government 12/17/2025 9:00:03 PM

Action Type Old Value New Value
Changed Due Date 
2021-04-16


 
2022-05-03

Modified Analysis by NIST 10/30/2025 3:55:58 PM

Action Type Old Value New Value
Added Reference Type 
CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855 Types: US Government Resource

CVE Modified by CISA-ADP 10/21/2025 8:17:28 PM

Action Type Old Value New Value
Added Reference 
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855

CVE Modified by CISA-ADP 10/21/2025 4:18:24 PM

Action Type Old Value New Value
Removed Reference 
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855

CVE Modified by CISA-ADP 10/21/2025 3:18:56 PM

Action Type Old Value New Value
Added Reference 
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855

Modified Analysis by NIST 3/07/2025 10:38:25 AM

Action Type Old Value New Value

CVE Modified by CISA-ADP 2/04/2025 3:15:40 PM

Action Type Old Value New Value
Added CWE 
CWE-918

CVE Modified by CVE 11/21/2024 12:56:53 AM

Action Type Old Value New Value
Added Reference 
http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html
Added Reference 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html
Added Reference 
http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html
Added Reference 
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html
Added Reference 
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855

CVE Modified by Microsoft Corporation 5/14/2024 4:36:44 AM

Action Type Old Value New Value

Modified Analysis by NIST 2/15/2024 3:18:22 PM

Action Type Old Value New Value

CVE Modified by Microsoft Corporation 12/29/2023 12:16:00 PM

Action Type Old Value New Value
Changed Description 
Microsoft Exchange Server Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-26412, CVE-2021-26854, CVE-2021-26857, CVE-2021-26858, CVE-2021-27065, CVE-2021-27078.


 
Microsoft Exchange Server Remote Code Execution Vulnerability
Added CVSS V3.1 
Microsoft Corporation AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CWE Remap by NIST 7/12/2022 1:42:04 PM

Action Type Old Value New Value
Changed CWE 
NVD-CWE-noinfo



CWE-918


Modified Analysis by NIST 5/06/2022 4:57:58 PM

Action Type Old Value New Value
Changed Reference Type 
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html No Types Assigned


 
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html Exploit, Third Party Advisory, VDB Entry

CVE Modified by Microsoft Corporation 5/21/2021 2:15:08 PM

Action Type Old Value New Value
Added Reference 
http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html [No Types Assigned]

Modified Analysis by NIST 5/21/2021 12:52:25 PM

Action Type Old Value New Value
Changed Reference Type 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html Exploit, Third Party Advisory


 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html Exploit, Third Party Advisory, VDB Entry
Changed Reference Type 
http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html No Types Assigned


 
http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html Exploit, Third Party Advisory, VDB Entry

CVE Modified by Microsoft Corporation 5/18/2021 2:15:07 PM

Action Type Old Value New Value
Added Reference 
http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html [No Types Assigned]

Modified Analysis by NIST 3/25/2021 10:33:03 PM

Action Type Old Value New Value
Changed CPE Configuration 
OR
 *cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*


 
OR
 *cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
Changed Reference Type 
http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html No Types Assigned


 
http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html Exploit, Third Party Advisory, VDB Entry
Changed Reference Type 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html No Types Assigned


 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html Exploit, Third Party Advisory

CVE Modified by Microsoft Corporation 3/23/2021 3:15:12 PM

Action Type Old Value New Value
Added Reference 
http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html [No Types Assigned]

CVE Modified by Microsoft Corporation 3/18/2021 12:15:14 PM

Action Type Old Value New Value
Added Reference 
http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html [No Types Assigned]

Initial Analysis by NIST 3/09/2021 12:58:57 PM

Action Type Old Value New Value
Added CVSS V3.1 
NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Added CVSS V2 
NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P)
Added CWE 
NIST NVD-CWE-noinfo
Added CPE Configuration 
OR
 *cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*
 *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
Changed Reference Type 
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855 No Types Assigned


 
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855 Patch, Vendor Advisory

Quick Info

CVE Dictionary Entry:
CVE-2021-26855
NVD Published Date:
03/02/2021
NVD Last Modified:
06/16/2026
Source:
Microsoft Corporation