CVE-2026-39993 in Download Station
Summary
by MITRE • 10/15/2026
A relative path traversal vulnerability has been reported to affect Download Station. If a remote attacker gains a user account, they can then exploit the vulnerability to read the contents of unexpected files or system data.
We have already fixed the vulnerability in the following version: Download Station 5.10.2.313 and later Download Station 5.11.3.322 and later
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Analysis
by VulDB Data Team • 10/15/2026
The reported issue constitutes a relative path traversal vulnerability within Synology's Download Station application, specifically affecting versions prior to the patched releases of 5.10.2.313 and 5.11.3.322. This class of security flaw typically arises when an application processes user-supplied input that specifies file paths without adequately sanitizing or validating relative path components such as dot-dot-slash sequences. In the context of a web-based download manager, this vulnerability allows for unauthorized access to files located outside the intended directory structure. The core technical failure lies in the insufficient validation of file path parameters passed by the client application during requests for downloading or managing files. When an attacker provides a crafted input containing relative navigation characters, the underlying server-side logic may resolve these paths incorrectly, leading the system to retrieve and serve content from arbitrary locations on the host filesystem rather than restricting access strictly to the designated download directories.
The operational impact of this vulnerability is significant because it enables information disclosure that can compromise the confidentiality of sensitive data stored on the NAS device. Although exploitation requires a valid user account with appropriate permissions, this prerequisite does not mitigate the severity for environments where multiple users have access or where privilege escalation might be possible through other vectors. An authenticated attacker could leverage this flaw to read configuration files, log entries, database dumps, or other system-critical data that should remain inaccessible. This exposure can facilitate further attacks by revealing internal network configurations, application secrets, or user credentials embedded in plaintext within accessible files. The ability to read unexpected files undermines the integrity and confidentiality guarantees expected from a secure file management service, potentially leading to broader security breaches if sensitive information is exfiltrated.
From a classification perspective, this vulnerability aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory, which describes flaws where software does not properly neutralize special elements within filenames or pathnames that can cause files to be located outside the intended directory. Additionally, in terms of tactical behavior, this exploitation technique corresponds to ATT&CK T1083: File and Directory Discovery, as it involves enumerating and accessing specific system resources to gather intelligence about the target environment. The attack vector is classified as remote with authentication requirements, placing it under MITRE ATT&CK TA0006: Credential Access or potentially TA0009: Collection depending on the ultimate goal of the attacker after gaining initial access through valid credentials.
To mitigate this risk, organizations must ensure that all instances of Download Station are updated to version 5.10.2.313 or later for the 5.10 branch, and version 5.11.3.322 or later for the 5.11 branch. These updates contain the necessary code changes to properly sanitize path inputs and enforce strict directory boundaries. In addition to applying vendor patches, administrators should adhere to the principle of least privilege by ensuring that user accounts associated with Download Station have minimal required permissions on the underlying operating system filesystem. Regular security audits and monitoring for unusual file access patterns can also help detect potential exploitation attempts before significant data loss occurs. Maintaining up-to-date software is critical as vendors continuously address such logic flaws through rigorous testing and secure coding practices to prevent unauthorized path resolution attacks.