What it is
CVE-2021-31207 is Microsoft Exchange Server Security Feature Bypass Vulnerability.
Vulnerability report
Exploited in the wild
Confirmed confidence
In CISA KEV
CVE-2021-31207
Microsoft Exchange Server Security Feature Bypass Vulnerability
Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 · affected before 15.00.1497.018
- Severity
- CVSS 6.6 · Medium
- Confidence
- Confirmed
- Exploit status
- Exploited in the wild
- EPSS
- 99.8%
- First observed
- —
- Last observed
- —
Decision summary
What security teams need to know first
Direct answers before the deeper technical record.
Is it exploited?
Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.
Who is affected?
Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 affected before 15.00.1497.018.
What should we do?
Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
Overview
Microsoft Exchange Server Security Feature Bypass Vulnerability
Microsoft Exchange Server Security Feature Bypass Vulnerability
Vendor
Product
Affected
Status
Microsoft
Microsoft Exchange Server 2013 Cumulative Update 23
Before 15.00.1497.018
Affected
Microsoft
Microsoft Exchange Server 2019 Cumulative Update 9
Before 15.02.0858.012
Affected
Microsoft
Microsoft Exchange Server 2016 Cumulative Update 20
Before 15.01.2242.010
Affected
Microsoft
Microsoft Exchange Server 2016 Cumulative Update 19
Before 15.01.2176.014
Affected
Microsoft
Microsoft Exchange Server 2019 Cumulative Update 8
Before 15.02.0792.015
Affected
- Published
- 11 May 2021
- Exploitation Reported
- 03 Nov 2021
- Attack vector
- Remote
- Complexity
- High
- Privileges
- High
- User interaction
- None
Tags
metasploit
cisa
ransomware
malware
microsoft
CVE References
- CVE Record CVE.org · CVE Record https://www.cve.org/CVERecord?id=CVE-2021-31207
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207 portal.msrc.microsoft.com · CVE Record https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CV...
- zerodayinitiative.com/advisories/ZDI-21-819 zerodayinitiative.com · CVE Record https://www.zerodayinitiative.com/advisories/ZDI-21-819/
- packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-R... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyS...
Exploitation evidence
Why KEV Intelligence marks this CVE as exploited
Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.
Exploited in the wild
CISA
Independent exploitation attestation added to the KEV Intelligence record.
Used in malware
CISA
Malware families have been linked to exploitation of this CVE.
Proof of concept available
Public scanner or PoC coverage increases practical exploitability.
Known exploited vulnerability sources
Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.
Learn about Pro API access| Source | Added |
|---|---|
| CISA First | 2021-11-03 00:00 UTC |
Detection
Operational artifacts and observed signals
Make the evidence actionable in scanner, SOC, and edge-control workflows.
Observed signals
- Request targets
- 0
- User-Agents
- 0
Raw values available in Pro and Enterprise.
Scanner coverage
Metasploit template detected 28 Apr 2025.
View Metasploit template (opens in new tab)Virtual patch status
No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.
Learn about virtual patches →Scanner Artifacts
Scanner and exploit-framework references linked to this CVE.
| Scanner | Reference | Detected |
|---|---|---|
| Metasploit | https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/exchange_proxyshell_rce.rb | 28 Apr 2025 |
Risk and context
Severity, weaknesses, and research context
CVSS v3.1
6.6
Medium
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
EPSS
99.8%
Potential Proof of Concepts
These PoCs are unverified and could contain malware. Use at your own risk.
Timeline
From disclosure to observed exploitation
-
Metasploit module available
Exploit module available
-
Public PoC available
Public proof-of-concept code published
-
Added to CISA KEV
Listed in the CISA Known Exploited Vulnerabilities catalog
-
First public exploitation report
Exploit observed in malware
-
CVE published
Vulnerability disclosed publicly
-
CVE ID reserved
Identifier reserved by the CNA
Pro API
Automate this intelligence
Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.
- Evidence confidence and provenance
- First-party sensor telemetry
- PoC and scanner references
- Affected versions and enrichment
- Automation-ready JSON delivery
GET /api/v2/pro/kevs/CVE-2021-31207
Free JSON includes basic KEV fields{
"cve_id": "CVE-2021-31207",
"confidence": "Confirmed",
"cvss_score": 6.6,
"cvss_estimated": false,
"epss_score": 0.99782,
"exploit_status": {
"exploited_in_the_wild": true,
"active_exploitation_observed": false
},
"sensor_telemetry": { "attempts": 0, "sensors": 0 }
}Early warning alerts
Get alerts on high-impact exploitation
Receive curator-selected alerts when exploitation activity warrants attention. Each alert includes the evidence and context needed to decide what requires attention now.