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

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):

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):

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":"<sha256>","api":{"token":"<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.