CVE-2025-66593: Synology Assistant Privilege Escalation

CVE-2025-66593 Overview

CVE-2025-66593 is an origin validation error vulnerability in Synology Assistant versions before 7.0.6-50085. The flaw allows local users to write arbitrary files with restricted content during the installation process. The weakness is categorized under [CWE-346: Origin Validation Error]. Exploitation requires local access and user interaction, which limits remote attack scenarios. Successful exploitation can affect file integrity and system availability on the host where the installer runs. Synology published advisory SA-25-17 to address the issue and released a fixed version.

Critical Impact
Local users can write arbitrary files containing restricted content during Synology Assistant installation, leading to potential integrity loss and disruption of system availability.

Affected Products

Synology Assistant versions prior to 7.0.6-50085
Windows, macOS, and Linux distributions of the Synology Assistant client
Systems where the vulnerable installer is executed by a local user

Discovery Timeline

2026-05-27 - CVE-2025-66593 published to the National Vulnerability Database (NVD)
2026-05-27 - Last updated in NVD database

Technical Details for CVE-2025-66593

Vulnerability Analysis

The vulnerability resides in the Synology Assistant installation routine. The installer does not properly validate the origin of resources used during setup. As a result, a local attacker can influence the installer to write files outside the intended scope. The written content is restricted in nature, meaning the attacker controls placement rather than fully arbitrary content. The impact concentrates on file integrity and process availability rather than confidentiality. The flaw maps to [CWE-346], which addresses failures to verify that a request or data source comes from the expected origin.

Root Cause

The root cause is missing or insufficient origin validation in the installer logic. Synology Assistant trusts input sources during installation without verifying their authenticity. This trust assumption allows a local user to direct the installer to write files in unintended locations. The advisory from Synology confirms the behavior and identifies the corrected version.

Attack Vector

The attack vector is local and requires user interaction. An attacker with local access must influence the installation process while a user runs Synology Assistant setup. There is no network-based exploitation path. Confidentiality is not impacted, but integrity is partially affected and availability can be fully disrupted on the target host. No public proof-of-concept code is currently available.

No verified exploit code is available. Refer to the Synology Security Advisory SA-25-17 for vendor technical details.

Detection Methods for CVE-2025-66593

Indicators of Compromise

Unexpected files written outside the standard Synology Assistant installation directory during or after setup execution
Installer process activity correlating with file writes to system or user-protected paths
Presence of Synology Assistant versions earlier than 7.0.6-50085 on managed endpoints

Detection Strategies

Inventory endpoints for installed versions of Synology Assistant and flag any build below 7.0.6-50085
Monitor process creation events for the Synology Assistant installer and correlate with file system writes outside expected paths
Alert on local user invocations of the installer followed by privilege-relevant file modifications

Monitoring Recommendations

Enable file integrity monitoring on directories targeted by application installers
Collect endpoint telemetry covering installer execution, child processes, and file write operations
Track software inventory changes through centralized asset management to catch unpatched Synology Assistant deployments

How to Mitigate CVE-2025-66593

Immediate Actions Required

Upgrade Synology Assistant to version 7.0.6-50085 or later on all endpoints
Restrict installer execution to administrative accounts where feasible
Audit endpoints for outdated Synology Assistant deployments and prioritize remediation

Patch Information

Synology has released Synology Assistant 7.0.6-50085 to address the vulnerability. Administrators should consult the Synology Security Advisory SA-25-17 for the official fix details and download instructions.

Workarounds

Avoid running the vulnerable Synology Assistant installer on shared or multi-user systems until patched
Limit local user privileges to reduce the population of accounts capable of influencing the installer
Remove Synology Assistant from systems where it is not required to eliminate the attack surface

bash

# Verify installed Synology Assistant version on Windows
(Get-ItemProperty "HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*" `
    | Where-Object { $_.DisplayName -like "Synology Assistant*" }) `
    | Select-Object DisplayName, DisplayVersion