CVE-2025-66592

File writes and denial of service via installer

Published May 27, 2026 · Updated May 27, 2026

Origin validation error in Synology Active Backup for Business Agent before 3.1.0-4967 allows local users to write files and cause denial of service. Synology has not disclosed which installer origin is trusted, how it is validated, or which restricted content can be written. Exploitation requires a local user to run a crafted installer; the documented consequences are restricted-content file writes and service interruption.

CVSS severity6.1
Medium
EPSS probability0.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in Synology Active Backup for Business Agent before 3.1.0-4967 allows local users to write files and cause denial of service. Synology has not disclosed which installer origin is trusted, how it is validated, or which restricted content can be written. Exploitation requires a local user to run a crafted installer; the documented consequences are restricted-content file writes and service interruption.

The record

CVE
CVE-2025-66592
Published
May 27, 2026
Updated
May 27, 2026
Vendor
Synology
Product
Active Backup for Business Agent
Classifications
CWE-346, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2026CVE publishedPublication date reported by the CVE source.
  2. May 27, 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=* <3.1.0-4967

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Synology · Active Backup for Business Agentversion=* <3.1.0-4967

Published CVSS scores

5.6NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:H
6.1SynologyCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-346Origin Validation Error
T1204.002User Execution: Malicious File

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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