CVE-2021-42321
Microsoft Exchange Server Remote Code Execution Vulnerability
- High 8.8
- Exploited: added to CISA KEV 17 Nov 2021
- Used in ransomware campaigns
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Key facts
- Published
- 10 Nov 2021
- Last changed
- 19 Aug 2026
- Assigned by
- microsoft
- KEV added
- 17 Nov 2021
- KEV fix due
- 1 Dec 2021
- Used in ransomware
- Yes, according to CISA
- EPSS
- 91.737% likely to be exploited in the next 30 days, higher than 99.819% of CVEs (scores for 15 Nov 2026)
- SSVC (CISA)
- Exploitation: active; Automatable: no; Technical impact: total
Severity scores
Each score is shown as its source gave it. They are not averaged or merged.
- 8.8CVSS 3.1, Highfrom the CNA (microsoft)
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
What to do
- Apply updates per vendor instructions.CISA KEV required action
Historical context and remediation
This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.
No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.
Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.
Affected products
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 21 |
|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 22 |
|
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 10 |
|
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 11 |
|
Timeline
- 10 Nov 2021 Published
- 17 Nov 2021 CVE-2021-42321 added to CISA KEV
- 17 Nov 2021 Added to the CISA KEV catalogue