CVE-2021-42321
HIGHCVSS 8.8/10Actively ExploitedEPSS 90.39%
Last modified
CVE-2021-42321 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. Microsoft Exchange Server Remote Code Execution Vulnerability. CISA has confirmed active exploitation in the wild. EPSS estimates a 90.39% chance of exploitation in the next 30 days.
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Metrics
Exploitation Status
This vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Federal agencies must remediate by .
Affected Software
| Vendor | Product | Versions | Update |
|---|---|---|---|
| Microsoft | Exchange Server | 2016 | Cumulative Update 21 |
| Microsoft | Exchange Server | 2019 | Cumulative Update 10 |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321Patch, Vendor Advisory
- https://packetstormsecurity.com/files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
- https://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
Timeline
- Published
- Last Modified
- Status
- Analyzed
Frequently Asked Questions
What is CVE-2021-42321?
Microsoft Exchange Server Remote Code Execution Vulnerability
How severe is CVE-2021-42321?
CVE-2021-42321 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 90.39% probability of exploitation in the next 30 days. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.
How do I fix CVE-2021-42321?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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Are you affected by CVE-2021-42321?
Run a free Strix scan to check your systems for this vulnerability.
Scan your code nowSource: NVD / NIST