CVE-2021-33766
Microsoft Exchange Server Information Disclosure Vulnerability
Microsoft Exchange Server Information Disclosure Vulnerability
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- Low
- Integrity
- Low
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
Microsoft Exchange Server Information Disclosure Vulnerability
Microsoft Exchange Server Information Disclosure Vulnerability
- Record
CVE-2021-33766- CVSS 3.1
- 7.3 High
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 - Updated
- 2026-11-02
EUVDEUVD-2021-20443
Microsoft Exchange Server Information Disclosure Vulnerability
- Record
EUVD-2021-20443- CVSS 3.1
- 7.3 High
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 - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-f9f4-96j3-5mvr
Microsoft Exchange Information Disclosure Vulnerability
Microsoft Exchange Information Disclosure Vulnerability
- Record
GHSA-f9f4-96j3-5mvr- CVSS 3.1
- 7.3 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L - Weakness
- CWE-287
- Updated
- 2026-11-02
CISA KEV No score
Microsoft Exchange Server Information Disclosure
Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.
- Record
CVE-2021-33766- Weakness
- CWE-287
- Updated
- 2026-11-02
NVD
Microsoft Exchange Server Information Disclosure Vulnerability
- Record
CVE-2021-33766- CVSS 3.1
- 7.3 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L - CVSS 3.1
- 7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N - CVSS 2.0
- 5.0 Medium
AV:N/AC:L/Au:N/C:P/I:N/A:N - Updated
- 2026-11-02
Affected products
Public exploits
Links only. Every CVE stores no exploit code.
| Source | Link | Date |
|---|---|---|
| PoC in GitHub | bhdresh/CVE-2021-33766 | 2021-08-31 |
| PoC in GitHub | demossl/CVE-2021-33766-ProxyToken | 2021-09-15 |
| Nuclei | Microsoft Exchange - Authentication Bypass |
History
| Recorded | Changed | Sources |
|---|---|---|
| exploitation, exploits | ||
| first indexed | CVE List, EUVD, GitHub Advisories, CISA KEV, Nuclei, NVD, PoC in GitHub |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-33766 is a high vulnerability (CVSS 7.3) in Microsoft Exchange Server, published July 14, 2021. CISA lists it as known to be exploited, since January 18, 2022. EUVD reports exploitation since January 18, 2022. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 98.2%, the 99th percentile. No source names a fixed version.
References
msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766
zerodayinitiative.com/advisories/ZDI-21-798
cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766
nvd.nist.gov/vuln/detail/CVE-2021-33766
github.com/advisories/GHSA-f9f4-96j3-5mvr