CVE-2026-40536: Synology DSM Path Traversal Vulnerability

CVE-2026-40536 Overview

CVE-2026-40536 is a path traversal vulnerability [CWE-22] in the Audio API of Synology DiskStation Manager (DSM). The flaw allows remote authenticated users to traverse outside the intended directory scope and read non-sensitive information from the underlying filesystem. Synology addressed the issue in DSM versions 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2.

The vulnerability requires valid credentials on the target DSM instance. Exploitation does not require user interaction and can be performed over the network against exposed DSM management interfaces.

Critical Impact

An authenticated remote attacker can read non-sensitive files outside the Audio API's intended directory scope by supplying crafted pathname input.

Affected Products

• Synology DiskStation Manager (DSM) versions before 7.2.1-69057-10
• Synology DiskStation Manager (DSM) versions before 7.2.2-72806-7
• Synology DiskStation Manager (DSM) versions before 7.3.2-86009-2

Discovery Timeline

• 2026-09-18 - CVE-2026-40536 published to NVD
• 2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-40536

Vulnerability Analysis

The Audio API in DSM fails to properly restrict user-supplied pathname input to the intended directory. An authenticated attacker can craft input containing directory traversal sequences to reference files outside the API's designated working directory. The vulnerability is limited to disclosure of non-sensitive information based on the vendor advisory, and it does not affect data integrity or system availability.

The attack vector is network-based and requires low privileges. No user interaction is required to trigger the flaw, which increases exposure for DSM instances reachable from untrusted networks or shared multi-user deployments.

Root Cause

The root cause is improper limitation of a pathname to a restricted directory, classified under [CWE-22]. The Audio API code path accepts a filename or path parameter and passes it to file access routines without canonicalizing the resulting path or validating it against a permitted base directory. Sequences such as ../ are not stripped or rejected before the file lookup.

Attack Vector

Exploitation requires a valid DSM user session. The attacker issues a request to the vulnerable Audio API endpoint with a path parameter containing traversal sequences. The DSM process then resolves the manipulated path and returns file contents or metadata from unintended locations. See the Synology Security Advisory SA-26-06 for vendor technical detail.

Detection Methods for CVE-2026-40536

Indicators of Compromise

• HTTP requests to DSM Audio API endpoints containing ../, ..%2f, or other encoded traversal sequences in path or filename parameters.
• Audio API responses returning unexpected file contents or file sizes inconsistent with legitimate audio resources.
• Authenticated sessions issuing high volumes of Audio API requests targeting varied file paths.

Detection Strategies

• Inspect DSM web server access logs for Audio API URIs containing traversal patterns, URL-encoded dot sequences, or absolute path references.
• Correlate authenticated user activity with anomalous file access patterns originating from the DSM Audio API service.
• Deploy signatures on network security tooling to flag path traversal payloads directed at DSM management interfaces.

Monitoring Recommendations

• Forward DSM system and web access logs to a centralized log platform for long-term retention and query.
• Alert on authenticated sessions issuing traversal-style parameters against any DSM API endpoint.
• Monitor for new or unusual user accounts on DSM appliances that subsequently interact with the Audio API.

How to Mitigate CVE-2026-40536

Immediate Actions Required

• Upgrade DSM to version 7.2.1-69057-10, 7.2.2-72806-7, 7.3.2-86009-2, or later as applicable to the deployed release branch.
• Restrict DSM management interface exposure to trusted networks and VPN-accessible ranges only.
• Audit DSM user accounts and revoke unnecessary or dormant credentials that could be used for authenticated exploitation.

Patch Information

Synology released fixed builds addressing this issue. Refer to the Synology Security Advisory SA-26-06 for the complete list of fixed versions and upgrade guidance. Apply the update through DSM Control Panel under Update & Restore or download the patch package directly from the Synology Download Center.

Workarounds

• Block external access to DSM administrative and API endpoints at the network perimeter until patching is complete.
• Enforce strong authentication and two-factor authentication on all DSM accounts to reduce the pool of attackers able to reach the Audio API.
• Disable or restrict the Audio Station package on systems where audio functionality is not required.

# Verify installed DSM version from the appliance shell
cat /etc.defaults/VERSION | grep -E "productversion|buildnumber|smallfixnumber"