---
id: CVE-2021-33766
title: Microsoft Exchange Server Information Disclosure Vulnerability
summary: Microsoft Exchange Server Information Disclosure Vulnerability
severity: high
cvss: 7.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L'
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-2021-33766'
references:
  - url: 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766'
    label: secure@microsoft.com
  - url: >-
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.zerodayinitiative.com/advisories/ZDI-21-798/'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - kev
  - in-the-wild
  - exploit-available
epss: 0.98136
epssPercentile: 0.99912
kev: true
kevDateAdded: '2022-01-18'
kevDueDate: '2022-02-01'
kevRansomware: false
exploited: true
zeroDay: true
ingestedAt: '2026-08-10T16:41:15.440Z'
exploits:
  github: 2
  githubRepos:
    - 'https://github.com/bhdresh/CVE-2021-33766'
    - 'https://github.com/demossl/CVE-2021-33766-ProxyToken'
  nuclei:
    - CVE-2021-33766
  checkedAt: '2026-09-24T07:52:48.016Z'
exploitAvailable: true
---

## Overview

Microsoft Exchange Server Information Disclosure 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.