CVE-2021-33766VulnerabilityPublished 01/18/2022Updated 10/24/2026

CVE-2021-33766: Microsoft Exchange Server Information Disclosure

Affects Microsoft Exchange ServerSource CISA KEV

Severity

High

No CVSS score published yet

Exploitation: Actively exploited – in CISA KEV since 01/18/2022
KEV deadline: 02/01/2022
EPSS: 98.2% chance of exploitation in 30 days – higher than 99% of CVEs

What to do

CISA required action

Apply updates per vendor instructions.

nvd.nist.gov/vuln/detail/CVE-2021-33766 (opens in a new tab)

Description

CVE-2021-33766 is an information disclosure vulnerability in Microsoft Exchange Server that allows an unauthenticated attacker to steal email traffic from the target system. This vulnerability has been exploited in the wild. No specific affected versions or patch information is provided in the available data.

Summary

Microsoft Exchange Server contains an information disclosure vulnerability identified as CVE-2021-33766. This flaw enables an unauthenticated attacker to access and steal email traffic from the affected Exchange Server. The vulnerability has been confirmed to be exploited in the wild. No detailed version or patch information is available in the provided data.

Impact

An unauthenticated attacker can exploit this vulnerability to steal email traffic from the targeted Microsoft Exchange Server, potentially leading to exposure of sensitive communications and data. The vulnerability is known to be actively exploited in the wild, increasing the risk to affected organizations.

Mitigation

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no patch or official fix information is provided, organizations should monitor Microsoft advisories closely and apply any updates or mitigations recommended by Microsoft promptly.

Weaknesses

CWE-287Improper Authentication (opens in a new tab)

What to do

Description

AnalysisAI-generated, updated 10/24/2026, 09:57:12 UTC

Weaknesses

References

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