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High 8.8Known exploited (CISA KEV)Published Nov 10, 2021
CVE-2021-42321Microsoft Exchange Server Remote Code Execution Vulnerability
Updated under an hour ago ()
Does this affect you?
It affects Microsoft Exchange Server 2016 Cumulative Update 21 and 4 other products. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Nov 17, 2021; federal agencies had to remediate by Dec 1, 2021, and it is known to be used in ransomware. Treat that date as your deadline.
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Microsoft Exchange Server Remote Code Execution Vulnerability
- CVSS
- 8.8 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
- Weakness (CWE)
- Not given
- Known exploited
- Added to CISA KEV Nov 17, 2021; federal remediation due Dec 1, 2021; known ransomware useApply updates per vendor instructions.
- EPSS (exploitation in the next 30 days)
- 91.74% (percentile 100)
- Assigned by
- microsoft
- NVD analysis
- Analyzed
- Record last updated
- Aug 19, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Microsoft Microsoft Exchange Server 2016 Cumulative Update 21 microsoft:exchange_server_2016_cumulative_update_21 (from the name) | from 15.01.0 before 15.01.2308.020 | CNA record |
Microsoft Microsoft Exchange Server 2016 Cumulative Update 22 microsoft:exchange_server_2016_cumulative_update_22 (from the name) | from 15.0.0 before 15.01.2375.017 | CNA record |
Microsoft Microsoft Exchange Server 2019 Cumulative Update 10 microsoft:exchange_server_2019_cumulative_update_10 (from the name) | from 15.02.0 before 15.02.0792.019 | CNA record |
Microsoft Microsoft Exchange Server 2019 Cumulative Update 11 microsoft:exchange_server_2019_cumulative_update_11 (from the name) | from 15.02.0 before 15.02.0986.014 | CNA record |
microsoft exchange_server microsoft:exchange_server | 2016; 2016; 2019; 2019 | NVD |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321vendor-advisory, patch
- http://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.htmlexploit, third-party-advisory, vdb-entry
- http://packetstormsecurity.com/files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.htmlexploit, third-party-advisory, vdb-entry
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321patch, vendor-advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.