CVE-2025-66592 Overview
CVE-2025-66592 is an origin validation error vulnerability [CWE-346] in Synology Active Backup for Business Agent before version 3.1.0-4967. The flaw allows local users to write arbitrary files with restricted content during installation of the agent software. Successful exploitation can compromise system integrity and availability on affected Windows hosts where the backup agent is deployed.
Critical Impact
Local users can leverage the installation process to write arbitrary files with restricted content, potentially impacting system availability and integrity.
Affected Products
- Synology Active Backup for Business Agent versions before 3.1.0-4967
- Windows hosts running the affected backup agent installer
- Endpoints protected by Synology backup infrastructure using the vulnerable agent
Discovery Timeline
- 2026-05-27 - CVE-2025-66592 published to NVD
- 2026-05-27 - Last updated in NVD database
Technical Details for CVE-2025-66592
Vulnerability Analysis
The vulnerability is classified as an origin validation error [CWE-346]. During the installation routine of Synology Active Backup for Business Agent, the installer does not properly verify the origin or source of inputs that determine file write operations. A local user can influence these operations to write files that would otherwise be restricted.
The attack vector is local and requires user interaction, consistent with exploitation occurring during the installation flow. While confidentiality is not impacted, the flaw permits limited integrity changes and a high impact to availability. This pattern is typical of installer-time file write abuses, where elevated installer context is misused to drop or modify files in privileged locations.
Root Cause
The root cause is insufficient validation of the originator of installation-time write requests. The installer trusts inputs without confirming they come from an authorized source, allowing a local attacker present on the system during installation to redirect or inject file write operations with restricted content.
Attack Vector
Exploitation requires local access to the target host and user interaction tied to the installer workflow. An attacker positioned on the system when an administrator initiates the Active Backup for Business Agent installation can influence the installer to write arbitrary files. The EPSS score of 0.004% reflects a low probability of widespread exploitation, but targeted abuse remains feasible in shared or multi-user environments.
No verified public proof-of-concept code is available. Refer to the Synology Security Advisory for vendor-supplied technical details.
Detection Methods for CVE-2025-66592
Indicators of Compromise
- Unexpected file writes to system or program directories during or immediately after Active Backup for Business Agent installation.
- Presence of Active Backup for Business Agent installations with versions older than 3.1.0-4967.
- Installer process spawning child operations that touch paths unrelated to the documented installation footprint.
Detection Strategies
- Inventory endpoints and identify any Synology Active Backup for Business Agent build below 3.1.0-4967.
- Audit installation logs for the agent to correlate install events with unexpected file system changes.
- Monitor for non-standard files created in agent install directories by users without administrative intent.
Monitoring Recommendations
- Enable file integrity monitoring on directories used by the Active Backup for Business Agent installer and runtime.
- Alert on installer executions originating from non-standard paths or unsigned wrappers.
- Track local privilege use and process lineage during software install operations on backup-enrolled endpoints.
How to Mitigate CVE-2025-66592
Immediate Actions Required
- Upgrade Synology Active Backup for Business Agent to version 3.1.0-4967 or later on all Windows endpoints.
- Restrict local user access on hosts where the agent is being installed to limit who can influence the installer.
- Verify installer integrity and run installations only from trusted, administrator-controlled sessions.
Patch Information
Synology has released a fixed version. Update to Active Backup for Business Agent 3.1.0-4967 or later. Full vendor guidance is available in the Synology Security Advisory SA_25_16.
Workarounds
- Defer installation or upgrade of the agent until the patched version is deployed across the environment.
- Limit interactive logon rights on systems scheduled for agent installation to reduce local attacker presence.
- Perform installations during maintenance windows where only authorized administrators are signed in.
# Check installed Active Backup for Business Agent version on Windows
wmic product where "Name like 'Active Backup for Business Agent%%'" get Name,Version
# Confirm version meets the patched baseline
# Required: 3.1.0-4967 or later
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
