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CVE-2021-42321

Microsoft Exchange Server Remote Code Execution Vulnerability

8.8 HighIn KEVPublic exploit

Microsoft Exchange Server Remote Code Execution Vulnerability

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

91.7%Up 90.8 points since Nov 10, 2021
90%50%10%1%

What each source reports

CVE List Score used 8.8

Microsoft Exchange Server Remote Code Execution Vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability

Record
CVE-2021-42321
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Updated
2026-11-02
EUVDEUVD-2021-29296 8.8

Microsoft Exchange Server Remote Code Execution Vulnerability

Record
EUVD-2021-29296
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Updated
2026-11-02
GitHub AdvisoriesGHSA-3f87-66x4-f3p7 8.8

Microsoft Exchange Server Remote Code Execution Vulnerability

Microsoft Exchange Server Remote Code Execution Vulnerability

Record
GHSA-3f87-66x4-f3p7
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
CISA KEV No score

Microsoft Exchange Server Remote Code Execution Vulnerability

An authenticated attacker could leverage improper validation in cmdlet arguments within Microsoft Exchange and perform remote code execution.

Record
CVE-2021-42321
Weakness
CWE-184, CWE-502
Updated
2026-11-02
NVD 8.8

Microsoft Exchange Server Remote Code Execution Vulnerability

Record
CVE-2021-42321
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
6.5 MediumAV:N/AC:L/Au:S/C:P/I:P/A:P
Updated
2026-11-02

Affected products

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHubDarkSprings/CVE-2021-423212021-11-23
MetasploitMicrosoft Exchange Server ChainedSerializationBinder RCE2021-12-09
PoC in GitHubtimb-machine-mirrors/testanull-CVE-2021-42321_poc.py2022-01-05
PoC in GitHub7BitsTeam/exch_CVE-2021-423212022-10-08

History

History
RecordedChangedSources
exploitation, exploits
first indexedCVE List, EUVD, GitHub Advisories, CISA KEV, Metasploit, NVD, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-42321 is a high vulnerability (CVSS 8.8) in Microsoft Exchange, published November 10, 2021. CISA lists it as known to be exploited, since November 17, 2021. EUVD reports exploitation since November 17, 2021. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 91.7%, the 99th percentile. No source names a fixed version.

References

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