CVE-2021-42321

Microsoft Exchange Server Remote Code Execution Vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability

Affected

Microsoft · Microsoft Exchange Server 2016 Cumulative Update 21 · Microsoft Exchange Server 2016 Cumulative Update 22 · Microsoft Exchange Server 2019 Cumulative Update 10 · Microsoft Exchange Server 2019 Cumulative Update 11

CVSS v3.1 NVD

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

CVSS v2.0 NVD

6.5 MEDIUMAV:N/AC:L/Au:S/C:P/I:P/A:P

EPSS

91.74% chance of exploitation in the next 30 days, 100th percentile

CISA KEV

added 2021-11-17, used in ransomware campaigns

Published

2021-11-10

Updated

2026-08-19

Proof-of-concept exploits (7)

• http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Executi…
• http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializatio…
• 7BitsTeam/exch_CVE-2021-4232110★ · 2022-10-08
• DarkSprings/CVE-2021-4232183★ · 2021-11-23
• timb-machine-mirrors/CVE-2021-42321_poc0★ · 2022-01-05
• timb-machine-mirrors/testanull-CVE-2021-42321_poc.py0★ · 2022-01-05
• pwntester/ysoserial.net3802★ · 2026-09-07

Metasploit modules (1)

• rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/exchange_chainedser…

Security advisories

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321

References

• CVE Record
• NVD entry

Related

• CVE-2022-23277
• CVE-2021-38639
• CVE-2021-38666
• CVE-2021-40444
• CVE-2021-40539
• CVE-2021-43267