CVE-2021-31207
KEVRansomware UseMicrosoft Exchange Server Security Feature Bypass Vulnerability
Description
Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass.
Microsoft Exchange Server Security Feature Bypass Vulnerability
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:HPublishedMay 11, 2021
Last modifiedJun 17, 2026
Added to KEVNov 3, 2021
Remediation dueNov 17, 2021
References
- packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlExploitThird Party Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207PatchVendor Advisory
- zerodayinitiative.com/advisories/ZDI-21-819/Third Party AdvisoryVDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207US Government Resource
0 recent articles mention this CVE
83
Risk assessment · Critical
Actively exploited and used by ransomware crews. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 1806 days
- Ransomware
- Used in known ransomware campaigns
- CVSS
- 6.6 MEDIUM
- EPSS (30-day exploit probability)
- 99.8% · top 1% of all CVEs
- Weakness
- CWE-434
- Attack vector
- Network, remotely reachable
Recommended actions
- 1.Apply updates per vendor instructions.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
- 5.Verify offline/immutable backups and segment the affected systems. This flaw is used for ransomware initial access.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.