Exploited vulnerability · CISA KEV
Is CVE-2021-31207 exploited? Yes: in CISA KEV since 3 Nov 2021
Gociux · Microsoft Exchange Server · data: CISA KEV, CVE record, FIRST EPSS
Yes. CVE-2021-31207, Microsoft Exchange Server Security Feature Bypass Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 176 days after it was published. It is known to be used in ransomware campaigns. It affects Microsoft Exchange Server. If you run it, CISA's required action is: Apply updates per vendor instructions.
exploitedYesCISA KEV · 3 Nov 2021
ransomwareKnownused in campaigns
EPSStop 1%among the most likely CVEs to be exploited
severity6.6CVSS 3.1 · medium
US federal due17 Nov 2021BOD 22-01 deadline
What it is
Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass.
| Vendor | Microsoft (391 exploited CVEs in KEV) |
| Product | Exchange Server |
| Vulnerability | Microsoft Exchange Server Security Feature Bypass Vulnerability |
| Weakness | CWE-20, CWE-434 |
| Published | 11 May 2021 |
| Added to KEV | 3 Nov 2021 |
| Reported by (CNA) | microsoft |
What to do
- Check whether you run it. Look for Exchange Server in your asset inventory, including appliances and cloud images. Stack check lists every exploited Microsoft CVE at once.
- Apply the fix. Apply updates per vendor instructions.
- If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 11 May 2021.
- Get told next time. Email alerts when CISA adds a CVE for Microsoft.
Other exploited CVEs in Exchange Server
- CVE-2023-21529: Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability (13 Apr 2026)
- CVE-2021-31196: Microsoft Exchange Server Information Disclosure Vulnerability (21 Aug 2024)
- CVE-2024-21410: Microsoft Exchange Server Privilege Escalation Vulnerability (15 Feb 2024)
- CVE-2022-41080: Microsoft Exchange Server Privilege Escalation Vulnerability (10 Jan 2023)
- CVE-2022-41082: Microsoft Exchange Server Remote Code Execution Vulnerability (30 Sep 2022)
- CVE-2022-41040: Microsoft Exchange Server Server-Side Request Forgery Vulnerability (30 Sep 2022)
References
Questions
Is CVE-2021-31207 being exploited?
Yes. CISA added CVE-2021-31207 to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, which means there is reliable evidence of exploitation in the wild.
Is CVE-2021-31207 used in ransomware attacks?
Yes, CISA lists it as known to be used in ransomware campaigns.
How do I fix CVE-2021-31207?
Apply updates per vendor instructions. Check Microsoft's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected Exchange Server and watch it for signs of compromise.
Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Microsoft scorecard · act-now radar.
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