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CVE-2021-31207

MEDIUM
6.6 RansomwareNVD

Summary

generated automatically from NVD data

CVE-2021-31207 is a security feature bypass vulnerability in Microsoft Exchange Server, affecting versions 2013, 2016 and 2019. It is associated with CWE-434, unrestricted upload of a file with a dangerous type. It carries a CVSS v3.1 score of 6.6 (MEDIUM), and the vector requires network access and high privileges. CISA lists it in its KEV catalog, added on 2021-11-03, with known use in ransomware campaigns.

NVD description

Microsoft Exchange Server Security Feature Bypass Vulnerability

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⚠️ Actively exploited — CISA KEV

This CVE was added to CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. It is confirmed exploited in the wild and must be patched as a priority.

Remediation deadline (US federal agencies): 2021-11-17

Used in known ransomware campaigns.

EPSS · FIRST.org

99.8%probability of exploitation in the next 30 days

Higher than 99% of scored CVEs

EPSS (Exploit Prediction Scoring System) estimates, from observed exploitation activity, how likely a CVE is to be exploited in the next 30 days. It complements CVSS, which measures severity, not likelihood. Score of 2026-10-19, recomputed daily by FIRST.org.

In-depth analysis on cveo.tech

We've published a detailed analysis of this CVE — exploitation, IOCs and mitigation.

CVSS v3.1 Score

6.6
/ 10.0
MEDIUM
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

Information

Published
11 mai 2021
Updated
17 juin 2026
Status
Analyzed
Source
secure@microsoft.com

Affected products

microsoft exchange server
Versions : 2013, 2016, 2019

Weaknesses (CWE)

CWE-434CWE-434

References (7)

Similar CVEs

Other vulnerabilities of type CWE-434

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