CVE-2021-33766Microsoft Exchange Server Information Disclosure Vulnerability
- 7.3HighCVSS base score
- 98.2%Exploitation in 30 daysEPSS · top 0.1% of all CVEs
- YesKnown exploitedin CISA's KEV since 18 Jan 2022
- 1Public exploitsMetasploit, Nuclei and Exploit-DB
Description
Microsoft Exchange Server Information Disclosure Vulnerability
Exploited in the wild
CISA lists this vulnerability in its Known Exploited Vulnerabilities catalog as Microsoft Exchange Server Information Disclosure.
- Added
- 18 Jan 2022
- Fix due (US federal)
- 1 Feb 2022
- Used by ransomware
- Not known
Apply updates per vendor instructions.
ENISA's EU Vulnerability Database lists it as exploited, from CISA's KEV, since 18 Jan 2022.
Public exploit
An exploit or proof of concept is public: anyone can try it against an unpatched system. The public collections list a Nuclei template for it. CISA's SSVC rates its exploitation: it is being exploited.
Show the exploits1
Nuclei templates1 template
- Microsoft Exchange - Authentication Bypass (Nuclei template) (opens in a new tab)
http/cves/2021/CVE-2021-33766.yamlSeverity high
Modules, templates and exploits as listed by the Metasploit Framework (BSD-3-Clause), ProjectDiscovery's Nuclei templates (MIT) and the Exploit Database (GPLv2), read once a day. Where the data comes from
Timeline
ID reserved
By microsoft
- 47 days later
· 47 days later
Published
- 6 months later
· 6 months later
Added to CISA KEV
Known exploited in the wild
- 5 years later
· 5 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| microsoftCNA (assigner) | 3.1 | High7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:U/RL:O/RC:C |
| NVDNVD · Analyzed | 3.1 | High7.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L |
- EPSS (exploitation in 30 days)
- 98.2% · top 0.1% of all CVEs (15 Nov 2026)
- CISA SSVC
- Exploitation: active · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.3.
Affected products
Microsoft · Microsoft Exchange Server 2013 Cumulative Update 23
- affected 15.00.0 – < 15.00.1497.015
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 19
- affected 15.01.0 – < 15.01.2176.012
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 20
- affected 15.01.0 – < 15.01.2242.008
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 8
- affected 15.02.0 – < 15.02.0792.013
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 9
- affected 15.02.0 – < 15.02.0858.010
References
References4
- Microsoft Exchange Server Information Disclosure Vulnerability (opens in a new tab)vendor-advisorypatch
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766 (opens in a new tab)x_refsource_MISCx_transferred
- https://www.zerodayinitiative.com/advisories/ZDI-21-798/ (opens in a new tab)x_refsource_MISCx_transferred
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766 (opens in a new tab)government-resource
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- CISA KEV catalog (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-20443 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-33766)Record last updated .