SiYuan Publish Reader Path Traversal via removeUnusedAttributeView

SiYuan, a note-taking application, is vulnerable to a path traversal attack through its publish service. The vulnerability lies in the /api/av/removeUnusedAttributeView endpoint, which can be accessed by users with RoleReader permissions. Publish requests are forwarded upstream with a valid JWT, bypassing intended access controls. The removeUnusedAttributeView handler accepts an attacker-controlled id parameter without proper validation and uses it in a file system delete operation. This allows attackers to use "../" sequences to traverse directories and delete arbitrary .json files within the SiYuan workspace. This vulnerability was disclosed on 2026-04-10 and impacts versions prior to the fix. Successful exploitation can lead to persistent destruction of Attribute View definitions, deletion of global workspace configuration, corruption of user state, and broken UI behavior.

Attack Chain

1. Attacker gains publish-reader access, or anonymous publish access if publish auth is disabled.
2. Attacker crafts a malicious POST request to /api/av/removeUnusedAttributeView with a path traversal payload in the id parameter, such as ../../../conf/conf.
3. The publish reverse proxy forwards the request to the kernel, injecting an X-Auth-Token with RoleReader.
4. The CheckAuth middleware allows the request because RoleReader is permitted.
5. The removeUnusedAttributeView handler extracts the attacker-controlled id value without validation.
6. The application constructs a file path using filepath.Join(util.DataDir, "storage", "av", id+".json"), resulting in a path outside the intended data/storage/av/ directory (e.g., <workspace>/conf/conf.json).
7. The application attempts to delete the file at the constructed path using filelock.RemoveWithoutFatal(absPath).
8. The targeted .json file is deleted, leading to persistent destruction of Attribute View definitions, deletion of global workspace configuration, or corruption of user state.

Impact

Successful exploitation of this vulnerability allows an attacker with publish-reader access to delete arbitrary .json files under the workspace path reachable from data/storage/av/. This can lead to persistent destruction of Attribute View definitions, deletion of global workspace configuration, deletion of local storage and outline state, corruption of user state that survives reload, and forced reset/recovery flows or broken UI behavior. The impact ranges from broken UI functionality to complete data loss and application instability.

Recommendation

• Deploy the "SiYuan Path Traversal Attempt" Sigma rule to detect attempts to exploit the vulnerability via the removeUnusedAttributeView endpoint.
• Block requests to /api/av/removeUnusedAttributeView containing path traversal sequences (e.g., ../) in the id parameter at the WAF or reverse proxy.
• Apply the remediation steps outlined in the advisory, specifically implementing input validation and subpath enforcement to prevent path traversal, as referenced in the Overview.