Microsoft Exchange Server Information Disclosure Vulnerability

cisa required action Apply updates per vendor instructions.

1. 2021-07-14 Published
2. 2022-01-18 Added to CISA KEV
3. 2022-02-01 CISA patch deadline
4. 2025-02-04 CISA SSVC: exploitation active

Added

4 y ago (2022-01-18)

Patch by

2022-02-01 (4 y ago)

Ransomware

Not known

Required action

Apply updates per vendor instructions.

Vendor, product

Microsoft, Exchange Server

CISA name

Microsoft Exchange Server Information Disclosure

Exploitation

Active, exploited in the wild

Automatable

yes

Technical impact

partial

Assessed

21 mo ago (2025-02-04)

98.18% chance of exploitation in the next 30 days, higher than 99.9% of all scored CVEs (FIRST EPSS, 2026-11-08).

• Nuclei template Microsoft Exchange - Authentication Bypass nuclei detection template

• Microsoft Microsoft Exchange Server 2013 Cumulative Update 23
• Microsoft Microsoft Exchange Server 2016 Cumulative Update 19
• Microsoft Microsoft Exchange Server 2016 Cumulative Update 20
• Microsoft Microsoft Exchange Server 2019 Cumulative Update 8
• Microsoft Microsoft Exchange Server 2019 Cumulative Update 9

Technology feeds

• Microsoft Exchange rss critical rss

• msrc.microsoft.com /update-guide/vulnerability/CVE-2021-33766

  vendor-advisory, patch

• portal.msrc.microsoft.com /en-US/security-guidance/advisory/CVE-2021-33766

  patch, vendor-advisory

• zerodayinitiative.com /advisories/ZDI-21-798/

  third-party-advisory, vdb-entry

• cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766

  government-resource, us-government-resource

• CVE List CVE-2021-33766
• NVD CVE-2021-33766

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.