CVE-2021-33766
KEVMicrosoft Exchange Server Information Disclosure
Description
Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.
Microsoft Exchange Server Information Disclosure Vulnerability
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:LPublishedJul 14, 2021
Last modifiedAug 10, 2026
Added to KEVJan 18, 2022
Remediation dueFeb 1, 2022
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766PatchVendor Advisory
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766PatchVendor Advisory
- zerodayinitiative.com/advisories/ZDI-21-798/Third Party AdvisoryVDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766US Government Resource
0 recent articles mention this CVE
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Risk assessment · High
Actively exploited. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 1729 days
- CVSS
- 7.3 HIGH
- EPSS (30-day exploit probability)
- 98.2% · top 1% of all CVEs
- Weakness
- NVD-CWE-noinfo
- Attack vector
- Network, remotely reachable
- Preconditions
- No privileges and no user interaction
Recommended actions
- 1.Apply updates per vendor instructions.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.