CVE-2025-4679Public exploitNetwork attack vector

Tenant data disclosure via leaked OAuth client secret

Published May 16, 2025 · Updated Jul 2, 2025

Credential exposure in Synology Active Backup for Microsoft 365 allows remote authenticated users to read Microsoft 365 tenant data. SynoOauth placed the global application's reusable client secret in the HTTP 302 Location header during OAuth setup. Access to that setup response exposed read-only group and Teams channel data across tenants that had granted the application permissions.

CVSS severity6.5
Medium
EPSS probability1.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Credential exposure in Synology Active Backup for Microsoft 365 allows remote authenticated users to read Microsoft 365 tenant data. SynoOauth placed the global application's reusable client secret in the HTTP 302 Location header during OAuth setup. Access to that setup response exposed read-only group and Teams channel data across tenants that had granted the application permissions.

The record

CVE
CVE-2025-4679
Published
May 16, 2025
Updated
Jul 2, 2025
Vendor
Synology
Product
Active Backup for Microsoft 365
Classifications
CWE-522, T1552
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Jul 2, 2025Record 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=N/A

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Synology · Active Backup for Microsoft 365version=N/A

Published CVSS scores

6.5Synology Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-522Insufficiently Protected Credentials
T1552Unsecured Credentials

Public exploit references

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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