CVE-2021-33766

Microsoft Exchange Server Information Disclosure

7.3 HIGHActively exploited (CISA KEV)EPSS 98.2%

Published14 Jul 2021
Added to CISA KEV18 Jan 2022
Remediation due1 Feb 2022

Description

Microsoft Exchange Server Information Disclosure Vulnerability

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityLow

IntegrityLow

AvailabilityLow

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Affected products

Microsoft Exchange Server2013 · 2016 · 2019

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

Patch & vendor advisories

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766PatchVendor Advisory
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766PatchVendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766US Government Resource
https://www.zerodayinitiative.com/advisories/ZDI-21-798/Third Party AdvisoryVDB Entry

Frequently asked

Is CVE-2021-33766 being actively exploited?

Yes. CVE-2021-33766 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 18 Jan 2022.

How severe is CVE-2021-33766?

CVE-2021-33766 has a CVSS 3.1 base score of 7.3, rated high. EPSS estimates a 98.2% probability of exploitation.

Which products are affected by CVE-2021-33766?

Affected products include Microsoft Exchange Server.

How do I fix CVE-2021-33766?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-33766 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.