---
id: CVE-2021-26857
title: Microsoft Exchange Server Remote Code Execution Vulnerability
summary: Microsoft Exchange Server Remote Code Execution Vulnerability
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-502
  - CWE-502
vendor: microsoft
product: exchange_server
affected:
  - exchange_server = 2010
  - exchange_server = 2013
  - exchange_server = 2016
  - exchange_server = 2019
published: '2021-03-03'
updated: '2026-08-12'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-26857'
references:
  - url: >-
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26857
    label: secure@microsoft.com
  - url: >-
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26857
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26857
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - kev
  - in-the-wild
  - exploit-available
epss: 0.95762
epssPercentile: 0.99871
kev: true
kevDateAdded: '2021-11-03'
kevDueDate: '2022-05-03'
kevRansomware: true
exploited: true
zeroDay: true
ingestedAt: '2026-08-12T19:54:25.677Z'
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/sirpedrotavares/Proxylogon-exploit'
  checkedAt: '2026-09-23T07:13:18.901Z'
exploitAvailable: true
---

## Overview

Microsoft Exchange Server Remote Code Execution Vulnerability

## Affected

- `exchange_server = 2010`
- `exchange_server = 2013`
- `exchange_server = 2016`
- `exchange_server = 2019`

## Remediation

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