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CVE-2021-31207

Microsoft Exchange Server Security Feature Bypass Vulnerability

MEDIUM
6.6
CVSS Score
Published: May 11, 2021 at 07:11 PM UTC
Updated: June 17, 2026 at 03:51 AM UTC
1 product affected across 1 vendorExchange Server

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Severity
MEDIUM6.6
Exploitation
CISA KEV
Exploit prediction
EPSS 100%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score99.8%

EPSS (Exploit Prediction Scoring System) estimates a 99.8% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

Microsoft Exchange Server contains an unspecified vulnerability that allows for security feature bypass.

Required Action
Apply updates per vendor instructions.
Ransomware Use
Known
Added to KEV
Nov 3, 2021
Remediation Due
Nov 17, 2021
1804 days overdue
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-31207

Description

Microsoft Exchange Server Security Feature Bypass Vulnerability

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Exchange Server· Microsoft
95%
15.00.0 ≤ v < 15.00.1497.01815.01.0 ≤ v < 15.01.2176.01415.01.0 ≤ v < 15.01.2242.01015.02.0 ≤ v < 15.02.0792.01515.02.0 ≤ v < 15.02.0858.01215.00.015.01.015.02.020132013 cumulative_update_2320162016 cumulative_update_192016 cumulative_update_2020192019 cumulative_update_82019 cumulative_update_9
Affected range stops below 15.00.1497.018, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2176.014, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2242.010, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0792.015, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0858.012, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (4)

x_refsource_MISCExploitThird Party AdvisoryVDB Entry
Source: [email protected]
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
x_refsource_MISCPatchVendor Advisory
Source: [email protected]
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31207
x_refsource_MISCThird Party AdvisoryVDB Entry
Source: [email protected]
https://www.zerodayinitiative.com/advisories/ZDI-21-819/
US Government Resource
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31207

SSVC — Action Prioritization

SSVCActiveNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.6MEDIUMmicrosoft
Vector?

Quick Info

StatusANALYZED
CWE
CWE-434

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