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CVE-2021-33766

Microsoft Exchange Server Information Disclosure Vulnerability

HIGH
7.3
CVSS Score
Published: July 14, 2021 at 05:53 PM UTC
Updated: August 10, 2026 at 07:58 PM UTC
1 product affected across 1 vendorExchange Server

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Severity
HIGH7.3
Exploitation
CISA KEV
Exploit prediction
EPSS 98%
SSVC
Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score98.2%

EPSS (Exploit Prediction Scoring System) estimates a 98.2% chance this CVE is exploited in the wild within the next 30 days — higher than 100% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

Microsoft Exchange Server contains an information disclosure vulnerability which can allow an unauthenticated attacker to steal email traffic from target.

Required Action
Apply updates per vendor instructions.
Ransomware Use
Unknown
Added to KEV
Jan 18, 2022
Remediation Due
Feb 1, 2022
1732 days overdue
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-33766

Description

Microsoft Exchange Server Information Disclosure Vulnerability

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Exchange Server· Microsoft
95%
15.00.0 ≤ v < 15.00.1497.01515.01.0 ≤ v < 15.01.2176.01215.01.0 ≤ v < 15.01.2242.00815.02.0 ≤ v < 15.02.0792.01315.02.0 ≤ v < 15.02.0858.01015.00.015.01.015.02.02013 cumulative_update_232016 cumulative_update_192016 cumulative_update_202019 cumulative_update_82019 cumulative_update_9
Affected range stops below 15.00.1497.015, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2176.012, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.01.2242.008, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0792.013, so it looks safe — our inference, not a vendor statement
Affected range stops below 15.02.0858.010, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (4)

PatchVendor Advisory
Source: [email protected]
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33766
Third Party AdvisoryVDB Entry
Source: [email protected]
https://www.zerodayinitiative.com/advisories/ZDI-21-798/
Vendor AdvisoryPatch
Source: cverecord
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33766
US Government Resource
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33766

SSVC — Action Prioritization

SSVCActiveAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.3HIGHmicrosoft
Vector?

Quick Info

StatusANALYZED
CWE
NVD-CWE-noinfo

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