CVE-2026-72792: SiYuan tag API information disclosure via password bypass

Executive brief

SiYuan is a popular note-taking and knowledge management application. The tag API endpoint fails to enforce password protection on published documents, allowing unauthorized readers to enumerate all tag labels and usage counts from password-protected documents they should not access. This leaks sensitive information such as project codenames, client names, and internal terminology that the document owner intended to keep confidential.

Technical details

The vulnerability is an incorrect authorization flaw in the tag filtering logic. The `getTag` endpoint calls `FilterTagsByPublishIgnore()` which validates only document visibility via `CheckPathAccessableByPublishIgnore()`, but does not verify the `CheckPublishAuthCookie()` required for password-protected documents. This is a tier mismatch: the project previously fixed an identical issue on the graph endpoint (commit 82e9ded42) by adding password-aware filtering, but the same pattern was not applied to the tag filter. An unauthenticated reader or one without the document password can POST to `/api/tag/getTag` and receive all tag labels with occurrence counts from protected documents. The endpoint requires only `CheckAuth()` middleware, no additional role or access checks. Patch available as of commit 4515fa257cfa.

Affected products

• SiYuan SiYuan < 0.0.0-20260726002639-4515fa257cfa

Timeline

• 2026-09-04: disclosed
• 2026-07-26: patched: Patch commit 4515fa257cfa released

References

• https://api.github.com/users/Shirshakhtml
• https://github.com/Shirshakhtml
• https://api.github.com/users/Shirshakhtml/gists%7B/gist_id%7D
• https://api.github.com/users/Shirshakhtml/repos
• https://avatars.githubusercontent.com/u/75179984?v=4
• https://api.github.com/users/Shirshakhtml/events%7B/privacy%7D