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CVE-2021-42321

97
FAUCET Score

CVE-2021-42321 is a critical Remote Code Execution (RCE) vulnerability affecting Microsoft Exchange Server. With a CVSS score of 8.8 (HIGH), it allows authenticated attackers to execute arbitrary code remotely with low attack complexity and no user interaction, leading to full compromise of confidentiality, integrity, and availability. This vulnerability is actively exploited in the wild, including by ransomware campaigns, and has publicly available exploit modules in Metasploit. The high EPSS score, FAUCET Risk Score, and extensive community discussion and media coverage highlight its significant threat and the urgent need for patching.

Impacted Technologies

VendorProductVersion(s)CPE
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*
2016CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*
2019CPE matchmatch criteria
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.8HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
90.39%
Probability of exploitation in next 30 days
EPSS Percentile
99.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Added to KEV · Nov 17, 2021
Metasploit: Microsoft Exchange Server ChainedSerializationBinder RCE · Dec 9, 2021
This CVE's current EPSS score of 0.9039 is in the 100th percentile among its peer group of 17,844 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.3 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (5)

microsoftpatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 21Fixed in: 15.01.2308.020
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 10Fixed in: 15.02.0792.019
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2016 Cumulative Update 22Fixed in: 15.01.2375.017
View patch
microsoftpatch availablevia msrc
Product: Microsoft Exchange Server 2019 Cumulative Update 11Fixed in: 15.02.0986.014
View patch

Vendor Advisories (1)

microsoft2021-Nov/CVE-2021-42321Important

Microsoft Exchange Server Remote Code Execution Vulnerability

Nov 9, 2021

References

cisa.gov / known-exploited-vulnerabilities-catalog
US Government Resource
packetstormsecurity.com / files/166153/Microsoft-Exchange-Server-Remote-Code-Execution.html
ExploitThird Party AdvisoryVDB Entry
packetstormsecurity.com / files/168131/Microsoft-Exchange-Server-ChainedSerializationBinder-Remote-Code-Execution.html
ExploitThird Party AdvisoryVDB Entry
portal.msrc.microsoft.com / en-US/security-guidance/advisory/CVE-2021-42321
PatchVendor Advisory