GHSA-p4m3-mgmm-c664 SiYuan: Path Traversal via Double URL Encoding in /assets/*path (publish mode arbitrary file─read), Incomplete fix of CVE-2026-41894

• Go github.com/siyuan-note/siyuan/kernel: < 0.0.0-20260628153353-2d5d72223df4 → fixed in 0.0.0-20260628153353-2d5d72223df4

Summary The patch for CVE-2026-41894 ("Path Traversal via Double URL Encoding") sanitized the `/export/` route but the **identical root cause remains in the `/assets/*path` route. In publish mode (anonymous read-only HTTP endpoint, default port 6808), an unauthenticated remote attacker can read arbitrary files inside `WorkspaceDir` — including `conf/conf.json` (which contains the `AccessAuthCode` SHA256 hash, API token, and sync keys), `temp/siyuan.db`, `temp/blocktree.db`, and `siyuan.log` — by double-URL-encoding `..` segments. Verified against siyuan v3.6.5: • `GET /assets/%252e%252e/%252e%252e/conf/conf.json` → HTTP 200, 10349 bytes (conf.json served) • `GET /export/%252e%252e/%252e%252e/conf/conf.json` → HTTP 401 (patched) • `GET /assets/%2e%2e/conf/conf.json` → HTTP 404 (single-decode handled correctly) ## Vulnerable Code Step 1 — route & first decode** (`kernel/server/serve.go:587-626`): The router registers `GET /assets/*path` for the publish listener. Gin performs one URL decoding pass on `URL.Path`, so a request for `/assets/%252e%252e/...` yields `context.Param("path") == "/%2e%2e/%2e%2e/conf/conf.json"` — literal `%2e%2e` strings, which `path.Clean` cannot collapse. Step 2 — second decode via fallback (`kernel/model/assets.go:536-563`, `GetAssetAbsPath`): ```go p, err := getAssetAbsPath(relativePath) if nil != err { // fallback decoded, e := url.PathUnescape(relativePath) // ← line 548, second decode if nil == e { p, err = getAssetAbsPath(decoded) } } ``` After the fallback decodes `%2e%2e` to `..`, `filepath.Join(DataDir, "../../conf/conf.json")` is `Clean`-ed to `WorkspaceDir/conf/conf.json`, an existing file. Step 3 — publish-mode access gate fall-through (`kernel/model/publish_access.go:288`, `CheckAbsPathAccessableByPublishAccess`): ```go if !filelock.IsSubPath(util.DataDir, absPath) { return true // ← fall-through allows anything outside DataDir but inside WorkspaceDir } ``` Because the resolved file is *outside* `DataDir` (it's in `WorkspaceDir`), the gate returns `true` and `IsSensitivePath()` is never invoked — `.db` / `.log` / `conf/` denylists do not apply to the `/assets/` route at all (unlike the patched `/export/` route, which additionally checks `IsSubPath(exportBaseDir, ...)`). Step 4 — file served (`http.ServeFile`): the request `URL.Path` contains literal `%2e%2e`, not `..`, so Go's `containsDotDot` guard passes and the file is sent. ## PoC Preconditions: siyuan kernel running with publish mode enabled (`conf.publish.enable = true`). Publish mode is the documented anonymous read-only endpoint for sharing notebooks. ``` $ curl -i "http://victim:6808/assets/%252e%252e/%252e%252e/conf/conf.json" HTTP/1.1 200 OK Content-Length: 10349 Content-Type: application/json ... {"appearance":{...},"editor":{...},"system":{...},"accessAuthCode":"","api":{"token":""}, ...} ``` Compared with the patched route: ``` $ curl -i "http://victim:6808/export/%252e%252e/%252e%252e/conf/conf.json" HTTP/1.1 401 Unauthorized ``` ## Root Cause Three independent flaws combine: 1. `GetAssetAbsPath` performs a second `url.PathUnescape` as a "compatibility" fallback, re-introducing the double-decode primitive that the CVE-2026-41894 patch eliminated on `/export/`. 2. `CheckAbsPathAccessableByPublishAccess` returns `true` for any path outside `DataDir`, even when that path is still inside `WorkspaceDir` (which contains `conf/conf.json`, `temp/*.db`, `siyuan.log`). 3. The `IsSensitivePath()` denylist applied to `/export/` is not called from the `/assets/` handler. ## Impact Unauthenticated remote arbitrary file read inside `WorkspaceDir`. Confirmed-readable files include: • `conf/conf.json` — `accessAuthCode` SHA256 (offline crackable), API token, S3/WebDAV sync credentials. • `temp/siyuan.db`, `temp/blocktree.db`, `temp/asset_content.db` — full notebook content (SQLite). • `siyuan.log` — internal paths, OS username, plugin info. Compromise of `accessAuthCode` / API token escalates to authenticated kernel API access (full read/write of all notebooks). Compromise of sync credentials escalates beyond the host. ## Fix 1. Remove the `url.PathUnescape` fallback in `GetAssetAbsPath` (assets.go:548), matching the `/export/` patch. 2. In `CheckAbsPathAccessableByPublishAccess`, replace the `IsSubPath(DataDir, ...)` fall-through with an explicit allowlist (only `DataDir` and its publishable subtree) and always call `IsSensitivePath()`. 3. Apply `IsSensitivePath()` inside the `/assets/*path` handler in `serve.go` as defense-in-depth. ## Status Privately reported via GitHub Security Advisory. PoC reproduced locally against v3.6.5 (publish port 6808): `GET /assets/%252e%252e/%252e%252e/conf/conf.json` returned HTTP 200 / 10349 bytes.