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
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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
- 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
- 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
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