CVE-2026-40535 in DiskStation Manager
Summary
by MITRE • 09/18/2026
An improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Desktop API in Synology DiskStation Manager (DSM) before 7.2.1-69057-10, 7.2.2-72806-7 and 7.3.2-86009-2 allows remote attackers to write limited files and conduct limited denial-of-service attacks.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified as an improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal, resides within the Desktop API component of Synology DiskStation Manager (DSM). This flaw affects multiple versions of the software, specifically DSM 7.2.1 prior to build 69057-10, DSM 7.2.2 prior to build 72806-7, and DSM 7.3.2 prior to build 86009-2. The core technical issue stems from insufficient validation of user-supplied input when processing file path requests directed at the Desktop API. In a secure implementation, any request involving file system operations must strictly sanitize inputs to ensure they remain within an intended base directory or sandboxed environment. However, in this vulnerable configuration, the application fails to adequately neutralize special characters such as dot-dot-slash sequences that are designed to navigate up the directory tree. This oversight allows an attacker to manipulate the path resolution logic, effectively breaking out of the restricted context and accessing files outside the permitted scope.
From a technical perspective, this flaw aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The Desktop API serves as an interface for managing desktop-related functionalities on Synology NAS devices, which are often exposed to network traffic in enterprise environments. When an attacker constructs a malicious request containing relative path traversal sequences, the server-side processing engine interprets these sequences literally rather than rejecting them or resolving them safely within the allowed boundary. This lack of strict input validation and canonicalization enables the remote exploitation of the vulnerability without requiring authentication in certain contexts, although some variants may require valid credentials depending on the specific API endpoint exposed. The ability to traverse directories undermines the fundamental security principle of least privilege by granting access beyond the intended application sandbox.
The operational impact of this vulnerability is multifaceted, primarily centering on unauthorized file system modifications and service disruption. Attackers can leverage this flaw to write limited files to arbitrary locations within the server's file system that are accessible via the API context. While the description notes limitations on what can be written, even restricted writes can have significant consequences in a network-attached storage environment. For instance, writing malicious scripts or configuration overrides could facilitate further attacks such as remote code execution if combined with other vulnerabilities like command injection. Furthermore, the vulnerability enables limited denial-of-service attacks. By repeatedly triggering file write operations to invalid paths or causing resource exhaustion through malformed requests, an attacker can degrade the performance of the DSM service or cause it to crash entirely, disrupting access to critical data stored on the NAS device for authorized users and organizations relying on its availability.
This type of vulnerability is frequently associated with MITRE ATT&CK technique T1083: File and Directory Discovery, as well as T1564: Hidden Files and Directories if used to conceal malicious artifacts. The exploitation vector typically involves crafting HTTP requests that manipulate query parameters or POST data containing the traversal sequences. Defense-in-depth strategies are essential for mitigating such risks beyond relying solely on application-level fixes. Organizations should ensure that their Synology NAS devices are updated to the latest patched versions, specifically DSM 7.2.1 build 69057-10 and later, DSM 7.2.2 build 72806-7 and later, or DSM 7.3.2 build 86009-2 and later. Additionally, network segmentation should be employed to restrict access to the management interfaces of NAS devices from untrusted networks. Web Application Firewalls can also provide a layer of protection by detecting and blocking common path traversal patterns in incoming traffic, although they are not a substitute for proper code-level remediation. Regular vulnerability scanning and patch management cycles are critical to maintaining the integrity and availability of these storage systems against evolving threat landscapes.