---
id: CVE-2021-34523
title: Microsoft Exchange Server Elevation of Privilege Vulnerability
summary: Microsoft Exchange Server Elevation of Privilege Vulnerability
severity: critical
cvss: 9
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N'
vendor: microsoft
product: exchange_server
affected:
  - exchange_server = 2013
  - exchange_server = 2016
  - exchange_server = 2019
published: '2021-07-14'
updated: '2026-08-10'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-34523'
references:
  - url: 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34523'
    label: secure@microsoft.com
  - url: >-
      http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34523
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.zerodayinitiative.com/advisories/ZDI-21-822/'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34523
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - kev
  - in-the-wild
  - exploit-available
epss: 0.9999
epssPercentile: 0.99985
kev: true
kevDateAdded: '2021-11-03'
kevDueDate: '2021-11-17'
kevRansomware: true
exploited: true
zeroDay: true
ingestedAt: '2026-08-10T16:41:17.511Z'
exploits:
  github: 2
  githubRepos:
    - 'https://github.com/mithridates1313/ProxyShell_POC'
    - 'https://github.com/SUPRAAA-1337/CVE-2021-34523'
  metasploit:
    - exploit/windows/http/exchange_proxyshell_rce
  checkedAt: '2026-09-08T15:36:49.431Z'
exploitAvailable: true
---

## Overview

Microsoft Exchange Server Elevation of Privilege Vulnerability

## Affected

- `exchange_server = 2013`
- `exchange_server = 2016`
- `exchange_server = 2019`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.