KEV Intelligence

Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2021-33766

Microsoft Exchange Server Information Disclosure Vulnerability

Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 · affected before 15.00.1497.015

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Severity
CVSS 7.3 · High
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
98.2%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-33766 is an unauthenticated Microsoft Exchange Server Information Disclosure Vulnerability.

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 affected before 15.00.1497.015.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Exchange Server Information Disclosure Vulnerability

Microsoft Exchange Server Information Disclosure Vulnerability

Vendor Product Affected Status
Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 Before 15.00.1497.015 Affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19 Before 15.01.2176.012 Affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20 Before 15.01.2242.008 Affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8 Before 15.02.0792.013 Affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9 Before 15.02.0858.010 Affected
View vendor advisory (opens in new tab)
Published
14 Jul 2021
Exploitation Reported
18 Jan 2022
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

microsoft cisa nuclei_scanner

CVE References

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 18 Jan 2022

Independent exploitation attestation added to the KEV Intelligence record.

Proof of concept available

GitHub

Recorded 31 Aug 2021

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

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Source Added
CISA First 2022-01-18 00:00 UTC
CVE 2026-08-10 15:31 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
0
User-Agents
0

Raw values available in Pro and Enterprise.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-33766.yaml 01 Jun 2026

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

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

EPSS

98.2%

All CVSS Scores

CVSS v3.1 7.3 High

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

CVSS v2.0 5.0 Medium

AV:N/AC:L/Au:N/C:P/I:N/A:N

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

bhdresh/CVE-2021-33766

github · Created 2021-08-31 22:03:13 UTC · 47 stars · AI assessment 90%

ProxyToken (CVE-2021-33766) : An Authentication Bypass in Microsoft Exchange Server POC exploit

Microsoft Exchange - Authentication Bypass

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. KEV confirmed by CVE

    Exploitation attested by an external source

  2. Nuclei template available

    Scanner coverage available

  3. Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  4. Public PoC available

    Public proof-of-concept code published

  5. CVE published

    Vulnerability disclosed publicly

  6. CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-33766

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2021-33766",
  "confidence": "Confirmed",
  "cvss_score": 7.3,
  "cvss_estimated": false,
  "epss_score": 0.98176,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

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