CVE-2026-54070: SiYuan: XSS in Bazaar README steals admin API token

## Summary `renderPackageREADME` in `kernel/bazaar/readme.go` renders a Bazaar package README from Markdown to HTML with the lute engine and `SetSanitize(true)`. The lute sanitizer is an event-handler blocklist: `allowAttr` rejects only attribute names present in a fixed `eventAttrs` map copied from the w3schools legacy handler list. That map omits modern event handlers. `onpointerover`, `onpointerdown`, `onauxclick`, `onbeforetoggle`, `onfocusin`, `onanimationstart`, and `ontransitionend` are not in the list, so the sanitizer passes them through verbatim on any tag. The frontend assigns the rendered HTML to `mdElement.innerHTML` in `app/src/config/bazaar.ts` with no client-side DOMPurify on this path, into a normal element in the main document (no iframe, no sandbox). The kernel sends no Content-Security-Policy, X-Frame-Options, or X-Content-Type-Options header on any response, so an inline handler runs when its event fires. The README is rendered when an Administrator opens a package in Settings → Marketplace, after the one-time marketplace trust consent. Install is not required. Result: a third-party Bazaar package author runs JavaScript in the Administrator's authenticated SiYuan origin when the Administrator views and interacts with the package listing, and gains full control of the workspace. ## Affected siyuan-note/siyuan, `<= 3.6.5` (latest release, 2026-04-21). Confirmed live-exploitable on the `b3log/siyuan:v3.6.5` image; identical code on `master` HEAD. Condition: the Administrator has accepted the marketplace trust consent (`bazaar.trust`, default false) and browses community Bazaar packages. The lute dependency pin is `github.com/88250/lute v1.7.7-0.20260419134724-bb68012f231d`. Both the online browse path (`getBazaarPackageREADME`) and the installed-package path (`getInstalledPlugin`) reach the same sink. ## Root cause `render/sanitizer.go:225-232` (lute): `allowAttr(name)` returns false only when `name` exists in the `eventAttrs` map, an attribute denylist rather than an allowlist. `render/sanitizer.go:235-334` (lute): `eventAttrs` is the w3schools handler list and contains no pointer, beforetoggle, focusin, animation, or transition handlers. `kernel/bazaar/readme.go:108-118`: `renderPackageREADME` builds the engine with `SetSanitize(true)` and returns the HTML string to the caller. `kernel/bazaar/readme.go:48-88`: `GetBazaarPackageREADME` renders an untrusted remote package README; `kernel/api/bazaar.go` exposes it at `/api/bazaar/getBazaarPackageREADME` (`router.go:423`, `CheckAuth`). `app/src/config/bazaar.ts:600` and `:609`: `mdElement.innerHTML = data.preferredReadme` / `= response.data.html`, no DOMPurify, target is a plain div. Kernel HTTP responses carry no CSP/X-Frame-Options/X-Content-Type-Options header (live-confirmed), so an inline handler is not blocked. ## Reproduction `b3log/siyuan:v3.6.5` Docker, default config, access auth code set, marketplace trust accepted. 1. Place a package whose README carries a non-blocklisted handler (an online community package produces the identical render at browse time): ``` mkdir -p workspace/data/plugins/evil-plugin cat > workspace/data/plugins/evil-plugin/plugin.json <<'JSON' {"name":"evil-plugin","author":"x","version":"1.0.0","minAppVersion":"3.0.0", "displayName":{"default":"Evil"},"description":{"default":"poc"}, "readme":{"default":"README.md"},"backends":["all"],"frontends":["all"]} JSON printf '<div onpointerover="alert(document.domain)">plugin description</div>\n' \ > workspace/data/plugins/evil-plugin/README.md ``` 2. Request the rendered README the way the Marketplace panel does: ``` curl -s -X POST http://127.0.0.1:6806/api/bazaar/getInstalledPlugin \ -H "Authorization: Token <API-TOKEN>" -H "Content-Type: application/json" \ -d '{"frontend":"all","keyword":""}' ``` Response `data.packages[].preferredReadme` contains the handler verbatim: ``` <div onpointerover="alert(document.domain)">plugin description</div> ``` A control `<img src=x onerror=...>` in the same README is returned HTML-escaped and inert. 3. In Settings → Marketplace, open the package and move the pointer over its README. Live-verified: the rendered HTML is assigned to `mdElement.innerHTML` (no CSP, no sandbox) and the `onpointerover` handler executes `alert(document.domain)` in the SiYuan origin on hover. Handlers do not auto-fire on insertion; one pointer/focus/click interaction on the listing triggers them. ## Impact - JavaScript execution in the Administrator's authenticated origin on a marketplace package view plus one hover/click/focus, no install needed. - Theft of the kernel API token (`conf.api.token`), which grants full Administrator API access. - Pivot to `installBazaarPlugin` and kernel control; the runtime image ships a shell. - A single malicious community package reaches every instance that views its listing. ## Credit Jan Kahmen, [turingpoint](https://turingpoint.de) (jan@turingpoint.de)

An adversary publishes a new Bazaar plugin — or pushes a malicious update to an already-trusted one — whose README.md embeds an inline handler such as `<div onpointerover="...">` that isn't present in lute's outdated event-handler denylist. An Administrator who has previously accepted the marketplace trust consent opens Settings → Marketplace to browse or review the package; the moment they move the pointer over, click, or tab-focus the rendered README element, the handler fires and attacker JavaScript executes in the fully authenticated SiYuan origin. The script reads the kernel API token from the local config, exfiltrates it to an attacker-controlled endpoint, and the attacker replays it against /api/bazaar/installBazaarPlugin and other admin APIs — including installing further plugins — to gain persistent, full workspace and container control, all without the Administrator ever installing the malicious package.