CVE-2023-21709Network attack vector

Unauthenticated privilege escalation

Published Aug 8, 2023 · Updated Aug 10, 2026

Privilege escalation in affected Microsoft Exchange Server 2016 and 2019 builds allows remote attackers to gain elevated privileges via network requests. Microsoft maps the issue to excessive authentication attempts but has not disclosed the affected authentication locus or erroneous operation. No credentials or user interaction are required, but the resulting privilege level and available administrative actions remain undisclosed.

CVSS severity9.8
Critical
EPSS probability1.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in affected Microsoft Exchange Server 2016 and 2019 builds allows remote attackers to gain elevated privileges via network requests. Microsoft maps the issue to excessive authentication attempts but has not disclosed the affected authentication locus or erroneous operation. No credentials or user interaction are required, but the resulting privilege level and available administrative actions remain undisclosed.

The record

CVE
CVE-2023-21709
Published
Aug 8, 2023
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Microsoft Exchange Server 2019 Cumulative Update 12
Classifications
CWE-307
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.02.0 <15.02.1118.037

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Exchange Server 2019 Cumulative Update 12version=15.02.0 <15.02.1118.037
Microsoft · Microsoft Exchange Server 2019 Cumulative Update 13version=15.02.0 <15.02.1258.025
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 23version=15.01.0 <15.01.2507.032

Published CVSS scores

9.8Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-307Improper Restriction of Excessive Authentication Attempts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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