CVE-2023-29357Known exploitationPublic exploitNetwork attack vector

Unauthenticated administrator access via unsigned proof tokens

Published Jun 13, 2023 · Updated Oct 21, 2025

Authentication bypass in Microsoft SharePoint Server 2019 before 16.0.10399.20005 allows remote attackers to obtain administrator privileges. SharePoint's OAuth token handling accepts a crafted hashed proof JWT using the none signing algorithm and fails to validate its signature and issuer correctly. No prior authentication or user interaction is required; a forged token permits impersonation of an administrator over the network.

CVSS severity9.8
Critical
EPSS probability99.98%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Microsoft SharePoint Server 2019 before 16.0.10399.20005 allows remote attackers to obtain administrator privileges. SharePoint's OAuth token handling accepts a crafted hashed proof JWT using the none signing algorithm and fails to validate its signature and issuer correctly. No prior authentication or user interaction is required; a forged token permits impersonation of an administrator over the network.

The record

CVE
CVE-2023-29357
Published
Jun 13, 2023
Updated
Oct 21, 2025
Vendor
Microsoft
Product
Microsoft SharePoint Server 2019
Classifications
CWE-303, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 13, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=16.0.0 <16.0.10399.20005

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft SharePoint Server 2019version=16.0.0 <16.0.10399.20005

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 IPsShadowserver observations through Sep 16, 2026. Gaps indicate unavailable data.
Sep 10, 2026Sep 16, 2026
View daily counts
Reporting dayUnique IPs
Sep 10, 20264
Sep 11, 20261
Sep 12, 20261
Sep 13, 2026Unavailable
Sep 14, 20261
Sep 15, 2026Unavailable
Sep 16, 2026Unavailable
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-303Incorrect Implementation of Authentication Algorithm
T1190Exploit Public-Facing Application

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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