SiYuan: Path Traversal via Double URL Encoding in `/export/` Endpoint (Incomplete Fix Bypass for CVE-2026-30869)

Summary

The fix for CVE-2026-30869 in SiYuan v3.5.10 only added a denylist check (IsSensitivePath) but did not address the root cause — a redundant url.PathUnescape() call in serveExport(). An authenticated attacker can use double URL encoding (%252e%252e) to traverse directories and read arbitrary workspace files including the full SQLite database (siyuan.db), kernel log, and all user documents.

Details

In kernel/server/serve.go, the serveExport() function (line 314-320) processes file paths as follows:

filePath := strings.TrimPrefix(c.Request.URL.Path, "/export/")
decodedPath, err := url.PathUnescape(filePath)     // second decode
fullPath := filepath.Join(exportBaseDir, decodedPath)

Go's HTTP server already decodes percent-encoded characters once during request parsing. The additional url.PathUnescape() call creates a double-decode vulnerability:

1. Attacker sends: GET /export/%252e%252e/siyuan.db
2. Go HTTP decodes %25 → %, result: URL.Path = /export/%2e%2e/siyuan.db
3. Go's path cleaner sees %2e%2e as literal characters (not ..), no redirect occurs
4. url.PathUnescape("%2e%2e") decodes to ..
5. filepath.Join(exportBaseDir, "../siyuan.db") resolves to <workspace>/temp/siyuan.db

The CVE-2026-30869 fix added IsSensitivePath() which blocks <workspace>/conf/ and OS-level paths (/etc, /root, etc.). However, it does NOT block:

• <workspace>/temp/siyuan.db — full document database
• <workspace>/temp/blocktree.db — block tree database
• <workspace>/temp/siyuan.log — kernel log
• <workspace>/temp/asset_content.db — asset content database

Note: the /appearance/ handler in the same file correctly uses gulu.File.IsSubPath() to validate paths (line 447), but this check is missing from the /export/ handler.

PoC

poc.zip Please extract the uploaded compressed file before proceeding

<img width="550" height="184" alt="스크린샷 2026-04-19 오후 5 08 30" src="https://github.com/user-attachments/assets/6aea4334-0b5a-4f45-bd1f-ecfad61ba524" />