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CVE-2026-4793 is a vulnerability in Synology Assistant, a desktop utility for managing Synology NAS devices across a local network. The flaw stems from an incorrect default permissions vulnerability that affects versions prior to 7.0.7-50095. During the installation process, the application writes critical files to the local file system but fails to restrict their default access permissions. This allows local users on the same machine—even those with low privileges—to read or write arbitrary files and conduct denial-of-service (DoS) attacks during installation.
The vulnerability is classified under CWE-276: Incorrect Default Permissions. It occurs because Synology Assistant creates temporary files and configuration elements with overly permissive settings, granting unnecessary access to local user accounts. This misconfiguration creates a window of opportunity for attackers to manipulate or read files that should remain protected. Local attackers can leverage these permissions to corrupt installation files, modify system configurations, or disrupt normal application functionality through carefully crafted file operations.
The vulnerability is particularly concerning because it affects systems where Synology Assistant is installed with default settings, making it a widespread concern across various deployments. The CVSS 3.1 base score is 7.3 (High), with the vector: AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H. This indicates a local attack vector, low attack complexity, low privileges required, and user interaction required, with high impacts on confidentiality, integrity, and availability.
The vulnerability was discovered by Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.. Synology has released a security update for the Assistant on Windows to address this vulnerability. The fixed release is version 7.0.7-50095 or above.
DailyCVE Form:
Platform: Synology Assistant
Version: < 7.0.7-50095
Vulnerability: Incorrect Default Permissions
Severity: High (CVSS 7.3)
Date: 2026-08-03
Prediction: Patch already released (2026-05-05)
What Undercode Say:
The vulnerability allows local users to perform unauthorized file operations and trigger denial-of-service during installation. The attack technique aligns with MITRE ATT&CK categories for initial access and privilege escalation, targeting local system compromise through configuration weaknesses. The vulnerability demonstrates the importance of secure coding practices and proper permission management in system-level applications.
Check current Synology Assistant version Windows: Check via "About" or registry reg query "HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall" /s | findstr "Synology Assistant" Check file permissions on installation directory (Windows example) icacls "C:\Program Files\Synology\SynologyAssistant" Monitor for suspicious file access during installation (Linux example) inotifywait -m -r /tmp/synology_install/
Exploit: (Educational Purposes!)
A local attacker with low privileges can exploit this vulnerability during the Synology Assistant installation process by:
1. Monitoring the installation directory for newly created files with weak permissions.
2. Writing malicious content to those files to corrupt the installation or achieve arbitrary file write.
3. Reading sensitive information from files that should have been restricted.
4. Overwriting critical installation files to cause a denial-of-service condition.
Example: Attempt to write to a file with weak permissions (conceptual) echo "malicious" > C:\ProgramData\Synology\Assistant\config.ini Example: Read sensitive configuration file type C:\ProgramData\Synology\Assistant\sensitive.dat
Protection:
- Upgrade to Synology Assistant version 7.0.7-50095 or above.
- Apply the principle of least privilege for all system components.
- Conduct security audits of existing installations to verify file permissions.
- Establish regular patch management procedures to ensure timely updates.
- Verify that all temporary files created during installation maintain appropriate access controls.
Impact:
- Confidentiality: Local users can read arbitrary files, potentially exposing sensitive information.
- Integrity: Local users can write arbitrary files, potentially modifying system configurations or injecting malicious content.
- Availability: Local users can conduct denial-of-service attacks by corrupting critical installation files.
- Privilege Escalation: The vulnerability can be leveraged for privilege escalation and unauthorized system modifications.
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Sources:
Reported By: nvd.nist.gov
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