CVE-2021-34523

highpriority · act · 90OT risk · criticalKEV · exploitedEPSS 1.000 · 100 %ileexploit · weaponizedDEEURUUS

grimoire priorityP0 · Act now

Exploitable?

Yes · in the wild

CISA KEV · 3 exploits · weaponized

Likely / severe?

100.0% (100th) EPSS

CVSS 7.5 · high

Is it mine?

28 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · cert_bund

added 2021-11-03remediate by 2021-11-17

required action Apply updates per vendor instructions.

EPSS · scored 2026-10-27

Microsoft Exchange Server Privilege Escalation Vulnerability

Microsoft Exchange Server Elevation of Privilege Vulnerability

remediations

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

A vendor fix is available.

FixedMicrosoft Exchange Server 2013 Cumulative Update 23msrc_csaf
15.00.1497.015:Security Update:https://support.microsoft.com/help/5001779
https://support.microsoft.com/help/5001779
FixedMicrosoft Exchange Server 2016 Cumulative Update 19msrc_csaf
15.01.2176.012:Security Update:https://support.microsoft.com/help/5001779
https://support.microsoft.com/help/5001779
FixedMicrosoft Exchange Server 2016 Cumulative Update 20msrc_csaf
15.01.2242.008:Security Update:https://support.microsoft.com/help/5001779
https://support.microsoft.com/help/5001779
FixedMicrosoft Exchange Server 2019 Cumulative Update 8msrc_csaf
15.02.0792.013:Security Update:https://support.microsoft.com/help/5001779
https://support.microsoft.com/help/5001779
FixedMicrosoft Exchange Server 2019 Cumulative Update 9msrc_csaf
15.02.0858.010:Security Update:https://support.microsoft.com/help/5001779
https://support.microsoft.com/help/5001779

cvss

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

9.8

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 7.5–9.8

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:Pprimary · NVD / NIST USexploitability 10 · impact 6.4

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:P/E:Hsecondary · CVSS-BT (t0sche)

v3.17.7highAV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Nsecondary · FSTEC (BDU) RU

v3.19criticalCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:Nsecondary · secure@microsoft.com USexploitability 2.5 · impact 5.8

v3.19criticalCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N/E:U/RL:O/RC:Csecondary · Microsoft Security Response Center US

v3.19criticalCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N/E:U/RL:O/RC:Csecondary · ENISA EU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · NVD / NIST USexploitability 3.9 · 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-264US

ATT&CK techniques

ATT&CK techniques this enables or maps to.

T1190Exploit Public-Facing Application — This privilege escalation vulnerability can be exploited by sending a specially crafted HTTP request to the exchange server, is it often chained together with CVE-2021-34473, a remote code execution vulnerability.exploitation

exploits (3)

Public proof-of-concept and weaponised exploit code.

exploit/windows/http/exchange_proxyshell_rceMicrosoft Exchange ProxyShell RCEweaponized · metasploit
SUPRAAA-1337/CVE-2021-34523test-yamlPoC · poc_in_github
mithridates1313/ProxyShell_POCPOC for scanning ProxyShell(CVE-2021-34523,CVE-2021-34473,CVE-2021-31207)PoC · poc_in_github

affected products (28)

Products and version ranges known to be affected.

Microsoft Exchange Server 2013 Cumulative Update 23all versionscert_bundDEcpe:/a:microsoft:exchange_server_2013::cumulative_update_23
Microsoft Exchange Server 2016 Cumulative Update 19all versionscert_bundDEcpe:/a:microsoft:exchange_server_2016:cumulative_update_19
Microsoft Exchange Server 2016 Cumulative Update 20all versionscert_bundDEcpe:/a:microsoft:exchange_server_2016:cumulative_update_20
Microsoft Exchange Server 2019 Cumulative Update 8all versionscert_bundDEcpe:/a:microsoft:exchange_server_2019:cumulative_update_8
Microsoft Exchange Server 2019 Cumulative Update 9all versionscert_bundDEcpe:/a:microsoft:exchange_server_2019:cumulative_update_9
Microsoft Microsoft Exchange Server 2013 Cumulative Update 2315.00.0 → 15.00.1497.015enisa_euvdEU
Microsoft Microsoft Exchange Server 2016 Cumulative Update 1915.01.0 → 15.01.2176.012enisa_euvdEU
Microsoft Microsoft Exchange Server 2016 Cumulative Update 2015.01.0 → 15.01.2242.008enisa_euvdEU
Microsoft Microsoft Exchange Server 2019 Cumulative Update 815.02.0 → 15.02.0792.013enisa_euvdEU
Microsoft Microsoft Exchange Server 2019 Cumulative Update 915.02.0 → 15.02.0858.010enisa_euvdEU
Microsoft Corp Microsoft Exchange Server≤ 2019 Cumulative Update 8fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2016 Cumulative Update 20fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2019 Cumulative Update 9fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2013 Cumulative Update 23fstec_bduRU
Microsoft Corp Microsoft Exchange Server≤ 2016 Cumulative Update 19fstec_bduRU
Microsoft Exchange Server 2013 Cumulative Update 23all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2013 Cumulative Update 23< 15.00.1497.015msrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 19all versionsfixedmsrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 19< 15.01.2176.012msrc_csafUS
Microsoft Exchange Server 2016 Cumulative Update 20all versionsfixedmsrc_csafUS

showing 20 of 28

advisories (2)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2024-1897Microsoft Exchange Server: Mehrere SchwachstellenDeutsch2021-07-13csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Microsoft Exchange Server 2013, Microsoft Exchange Server 2016 und Microsoft Exchange Server 2019 ausnutzen, um beliebigen Programmcode auszuführen, um seine Privilegien zu erhöhen und um Informationen offenzulegen.
msrc_CVE-2021-34523Microsoft Exchange Server Elevation of Privilege Vulnerability2021-07-13csaf · 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 cert_bund msrc_csaf NVD CVE.org MITRE

published 2021-07-14modified 2026-08-10

references (12)

External citations — patches, advisories, analysis.

scry

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