CVE-2026-6205 Overview
CVE-2026-6205 is an external control of file name or path vulnerability [CWE-73] in the Upload API of Synology DiskStation Manager (DSM). The flaw allows remote authenticated users to write arbitrary files to the underlying file system. Attackers can leverage this behavior to conduct denial-of-service attacks against affected appliances. Synology addressed the issue in DSM versions 7.2.1-69057-12, 7.2.2-72806-9, 7.3.2-86009-4, and 7.4-90075.
Critical Impact
Authenticated attackers on the network can write files to attacker-controlled paths and disrupt availability of the DiskStation appliance.
Affected Products
- Synology DiskStation Manager (DSM) versions before 7.2.1-69057-12
- Synology DiskStation Manager (DSM) versions before 7.2.2-72806-9
- Synology DiskStation Manager (DSM) versions before 7.3.2-86009-4 and 7.4-90075
Discovery Timeline
- 2026-09-18 - CVE-2026-6205 published to NVD
- 2026-09-18 - Last updated in NVD database
Technical Details for CVE-2026-6205
Vulnerability Analysis
The vulnerability resides in the Upload API component of Synology DSM. The API accepts a filename or path parameter from the client without sufficient validation. An authenticated remote user can supply crafted path values that influence where the uploaded file is written on disk. This behavior enables arbitrary file write outside the intended upload directory. Depending on the destination, the attacker can overwrite configuration files, log files, or other resources required for normal service operation, resulting in denial of service.
The weakness is classified under [CWE-73]: External Control of File Name or Path. The issue does not directly expose confidential data, but integrity and availability of the appliance are impacted.
Root Cause
The Upload API trusts client-controlled path information when determining the write destination. Missing canonicalization and path validation allow inputs that traverse directories or reference sensitive locations on the DSM file system.
Attack Vector
Exploitation requires network access to the DSM web interface and valid authenticated credentials. The attacker sends a crafted upload request that manipulates the file name or path parameter accepted by the API. No user interaction is required beyond the attacker's own session. Refer to the Synology Security Advisory SA-26-13 for vendor technical detail.
No public proof-of-concept has been observed. The EPSS probability at publication was 0.518%.
Detection Methods for CVE-2026-6205
Indicators of Compromise
- Unexpected files appearing outside standard upload directories on DSM volumes.
- Modified or truncated DSM configuration or system files that correlate with recent Upload API activity.
- DSM services failing to start or restarting unexpectedly following authenticated upload requests.
Detection Strategies
- Inspect DSM web server access logs for Upload API requests containing path traversal sequences such as ../ or absolute path values in filename parameters.
- Correlate authenticated user sessions with file write events at unusual file system locations.
- Alert on newly created files in DSM system directories that were not produced by package updates or scheduled maintenance.
Monitoring Recommendations
- Forward DSM access, authentication, and system logs to a centralized SIEM for retention and correlation.
- Baseline normal Upload API traffic patterns per user and flag deviations in payload size, target path, or frequency.
- Monitor for account activity from unusual source addresses, especially administrative accounts.
How to Mitigate CVE-2026-6205
Immediate Actions Required
- Upgrade DSM to version 7.2.1-69057-12, 7.2.2-72806-9, 7.3.2-86009-4, or 7.4-90075 as applicable to the deployed release train.
- Audit DSM user accounts and remove or disable unused accounts that could be used for authenticated exploitation.
- Restrict administrative and file-service accounts to strong, unique passwords with multi-factor authentication.
Patch Information
Synology has released fixed DSM builds addressing CVE-2026-6205. Administrators should apply the vendor-supplied updates documented in the Synology Security Advisory SA-26-13. Package updates can be applied through Control Panel > Update & Restore in the DSM interface.
Workarounds
- Limit DSM web interface exposure to trusted networks or a VPN until patches are applied.
- Restrict Upload API access to accounts that specifically require it and remove upload privileges from general users.
- Enable IP auto-block and account protection features in DSM to reduce credential abuse against exposed appliances.
# Verify installed DSM version from the CLI
cat /etc.defaults/VERSION | grep -E 'productversion|buildnumber|smallfixnumber'
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.