CVE-2021-42321

mediumpriority · act · 90OT risk · criticalKEV · exploitedEPSS 0.917 · 100 %ileexploit · weaponizedEURUUS

grimoire priorityP0 · Act now

Exploitable?

Yes · in the wild

CISA KEV · 4 exploits · weaponized

Likely / severe?

91.7% (100th) EPSS

CVSS 6.5 · medium

Is it mine?

18 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · msrc_csaf

added 2021-11-17remediate by 2021-12-01

required action Apply updates per vendor instructions.

EPSS · scored 2026-10-27

Microsoft Exchange Server Remote Code Execution Vulnerability

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

FixedMicrosoft Exchange Server 2016 Cumulative Update 21msrc_csaf
15.01.2308.020:Security Update:https://support.microsoft.com/help/5007409
https://support.microsoft.com/help/5007409
FixedMicrosoft Exchange Server 2016 Cumulative Update 22msrc_csaf
15.01.2375.017:Security Update:https://support.microsoft.com/help/5007409
https://support.microsoft.com/help/5007409
FixedMicrosoft Exchange Server 2019 Cumulative Update 10msrc_csaf
15.02.0792.019:Security Update:https://support.microsoft.com/help/5007409
https://support.microsoft.com/help/5007409
FixedMicrosoft Exchange Server 2019 Cumulative Update 11msrc_csaf
15.02.0986.014:Security Update:https://support.microsoft.com/help/5007409
https://support.microsoft.com/help/5007409

cvss

Technical severity, 0–10. One row per scoring source.

9.9

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–critical · 6.5–9.9

v2.06.5mediumAV:N/AC:L/Au:S/C:P/I:P/A:Pprimary · NVD / NIST USexploitability 8 · impact 6.4

v2.06.5mediumAV:N/AC:L/Au:S/C:P/I:P/A:P/E:Hsecondary · CVSS-BT (t0sche)

v3.19.9criticalAV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.18.8highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsecondary · secure@microsoft.com USexploitability 2.8 · impact 5.9

v3.18.8highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:Csecondary · Microsoft Security Response Center US

v3.18.8highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:Csecondary · ENISA EU

v3.18.8highCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsecondary · NVD / NIST USexploitability 2.8 · impact 5.9

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: active · Automatable: no · Technical Impact: totalcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-20US

ATT&CK techniques

ATT&CK techniques this enables or maps to.

exploits (4)

Public proof-of-concept and weaponised exploit code.

exploit/windows/http/exchange_chainedserializationbinder_rceMicrosoft Exchange Server ChainedSerializationBinder RCEweaponized · metasploit
7BitsTeam/exch_CVE-2021-423217BitsTeam/exch_CVE-2021-42321PoC · poc_in_github
DarkSprings/CVE-2021-42321Microsoft Exchange Server PocPoC · poc_in_github
timb-machine-mirrors/testanull-CVE-2021-42321_poc.pyClone from gistPoC · poc_in_github

affected products (18)

Products and version ranges known to be affected.

Microsoft Microsoft Exchange Server 2016 Cumulative Update 2115.01.0 → 15.01.2308.020enisa_euvdEU
Microsoft Microsoft Exchange Server 2016 Cumulative Update 2215.0.0 → 15.01.2375.017enisa_euvdEU
Microsoft Microsoft Exchange Server 2019 Cumulative Update 1015.02.0 → 15.02.0792.019enisa_euvdEU
Microsoft Microsoft Exchange Server 2019 Cumulative Update 1115.02.0 → 15.02.0986.014enisa_euvdEU
Microsoft Corp Microsoft Exchange Server≤ 2019 Cumulative Update 10fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2016 Cumulative Update 22fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2019 Cumulative Update 11fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2016 Cumulative Update 21fstec_bduRU
Microsoft Exchange Server 2016 Cumulative Update 21all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 21< 15.01.2308.020msrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 22all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 22< 15.01.2375.017msrc_csafUS
Microsoft Exchange Server 2019 Cumulative Update 10all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2019 Cumulative Update 10< 15.02.0792.019msrc_csafUS
Microsoft Exchange Server 2019 Cumulative Update 11all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2019 Cumulative Update 11< 15.02.0986.014msrc_csafUS
microsoft exchange server= 2016nvdUScpe:2.3:a:microsoft:exchange_server:*:*:*:*:*:*:*:*
microsoft exchange server= 2019nvdUScpe:2.3:a:microsoft:exchange_server:*:*:*:*:*:*:*:*

advisories (1)

Vendor and ecosystem advisories describing this.

msrc_CVE-2021-42321Microsoft Exchange Server Remote Code Execution Vulnerability2021-11-09csaf · msrc_csafUS
To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu msrc_csaf nvd NVD CVE.org MITRE

published 2021-11-10modified 2026-08-24

references (17)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

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