CVE-2026-85578 in SiYuan
Summary
by MITRE • 09/04/2026
SiYuan through 3.8.1 contains an authorization bypass vulnerability in the /api/file/getFile endpoint that allows readers to retrieve files from notebooks explicitly configured as Visible:false. Attackers with reader role can access private workspace files including notebook metadata and internal configuration by knowing the hidden notebook identifier and file path.
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Analysis
by VulDB Data Team • 09/04/2026
The SiYuan note-taking application, specifically through version 3.8.1, contains a critical authorization bypass vulnerability within its API endpoint responsible for retrieving file contents. This flaw resides in the /api/file/getFile route, which is designed to serve files associated with user notebooks. The core technical deficiency lies in the server-side access control logic, which fails to adequately verify whether the requesting user possesses sufficient privileges relative to the specific notebook being accessed. While SiYuan implements a visibility setting for notebooks that allows users to mark certain workspaces as private or hidden by setting their status to Visible:false, this configuration is not strictly enforced during file retrieval operations. Consequently, if an attacker can ascertain the unique identifier of a hidden notebook and the path of a target file within it, they can bypass the intended privacy controls simply by constructing a valid API request with appropriate authentication credentials for a lower-privileged role.
This vulnerability primarily affects users operating under the reader or guest roles who are granted limited access to shared notebooks but should not have visibility into private workspaces belonging to other users. The attacker leverages this misconfiguration to extract sensitive data that was explicitly intended to remain inaccessible. By exploiting the lack of proper authorization checks, an adversary can retrieve notebook metadata, internal configuration files, and arbitrary content stored within these hidden notebooks. This capability effectively nullifies the privacy guarantees provided by the Visible:false setting, allowing for unauthorized disclosure of confidential information such as personal notes, project details, or organizational secrets that were never meant to be shared with readers.
From a security classification perspective, this issue aligns closely with CWE-285, which describes Improper Authorization, where an actor is able to access resources they should not have permission to view. Furthermore, the exploitation technique maps directly to MITRE ATT&CK tactic T1078, specifically Valid Accounts and potentially T1530 if data exfiltration from cloud storage or local file systems is involved in broader attack scenarios involving this vulnerability. The ability to enumerate hidden notebook identifiers suggests that additional reconnaissance techniques might be employed by attackers to discover these IDs through other API endpoints or error messages before attempting the actual file retrieval, thereby facilitating a more comprehensive information disclosure campaign against targeted users.
The operational impact of this vulnerability extends beyond simple data leakage; it undermines user trust in the application's security model and can lead to significant privacy violations depending on the sensitivity of the stored content. For organizations using SiYuan for collaborative work, this flaw could result in the exposure of proprietary strategies or confidential employee information if hidden notebooks are used to segregate sensitive projects from general team access. The ease of exploitation means that even users with minimal technical expertise can potentially compromise data integrity and confidentiality by simply guessing or obtaining notebook IDs through social engineering or other side-channel attacks combined with this API flaw.
To mitigate this risk, immediate action is required on the part of both developers and end-users. SiYuan should release a patched version that enforces strict access control checks at the /api/file/getFile endpoint, ensuring that any request to retrieve files from notebooks marked as Visible:false is rejected unless the requester holds an owner or editor role with explicit permission for that specific notebook. Developers must implement robust authorization middleware that validates user permissions against resource ownership before processing file retrieval requests. For users currently running vulnerable versions, it is advisable to restrict sharing settings of sensitive notebooks and avoid storing highly confidential data in shared workspaces until a patch is available. Additionally, implementing rate limiting on API endpoints can help mitigate brute-force attempts to discover hidden notebook identifiers, adding an extra layer of defense against enumeration attacks that often precede such exploitation.