CVE-2021-42321 — Microsoft Exchange Server Remote Code Execution Vulnerability
Microsoft Exchange Server Remote Code Execution Vulnerability
Published
2021-11-10T00:47:43.000Z
Last modified
2025-10-21T23:25:25.274Z
CVSS vector
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
CISA KEV — Actively Exploited
01What is this vulnerability?
Microsoft Exchange Server Remote Code Execution Vulnerability
02Affected products
| Vendor | Product | Versions |
|---|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 21 | 15.01.0 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 10 | 15.02.0 |
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 22 | 15.0.0 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 11 | 15.02.0 |
03Active exploitation status
Yes — actively exploited. Added to the CISA KEV catalog on 2021-11-17. Ransomware use: Known.
04Recommended remediation
- Patch to a fixed version listed in the vendor advisory (see references below).
- Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
- Hunt historical logs for exploitation indicators — see Detection signatures below.
05Technical details
For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.
06Detection signatures
Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:
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07Related CVEs
No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.
08Timeline
- Published: 2021-11-10T00:47:43.000Z
- Last modified: 2025-10-21T23:25:25.274Z
- Added to CISA KEV: 2021-11-17
- BOD 22-01 due: 2021-12-01
09References
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