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CVE-2021-31207

97
FAUCET Score

CVE-2021-31207 is a critical Security Feature Bypass vulnerability affecting Microsoft Exchange Server, allowing for remote code execution. This high-severity flaw, with a CVSS score of 6.6, is easily exploitable over the network with high privileges and low attack complexity, leading to complete compromise of confidentiality, integrity, and availability. It is actively exploited in the wild, notably by ransomware campaigns and state-sponsored actors, with public exploit modules available in Metasploit. The vulnerability has garnered significant community and media attention, underscoring its widespread impact and the urgency for patching.

Impacted Technologies

VendorProductVersion(s)CPE
2013CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_20:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_9:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.6MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
HIGH
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
0.7
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
99.78%
Probability of exploitation in next 30 days
EPSS Percentile
100.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Added to KEV · Nov 3, 2021
Metasploit: Microsoft Exchange ProxyShell RCE · Apr 6, 2021
This CVE's current EPSS score of 0.9978 is in the 100th percentile among its peer group of 687 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.2 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.2 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

microsoftpatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2013 Cumulative Update 23Fixed in: 15.00.1497.018
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 9Fixed in: 15.02.0858.012
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 20Fixed in: 15.01.2242.010
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 19Fixed in: 15.01.2176.014
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 8Fixed in: 15.02.0792.015
View patch

Vendor Advisories (1)

microsoft2021-May/CVE-2021-31207Moderate

Microsoft Exchange Server Security Feature Bypass Vulnerability

May 11, 2021

References

cisa.gov / known-exploited-vulnerabilities-catalog
US Government Resource
packetstormsecurity.com / files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
ExploitThird Party AdvisoryVDB Entry
portal.msrc.microsoft.com / en-US/security-guidance/advisory/CVE-2021-31207
PatchVendor Advisory
zerodayinitiative.com / advisories/ZDI-21-819
Third Party AdvisoryVDB Entry