CVE-2026-30921: OneUptime Synthetic Monitor RCE via exposed Playwright browser object

Summary

OneUptime Synthetic Monitors allow low-privileged project users to submit custom Playwright code that is executed on the oneuptime-probe service. In the current implementation, this untrusted code is run inside Node's vm and is given live host Playwright objects such as browser and page.

This creates a distinct server-side RCE primitive: the attacker does not need the classic this.constructor.constructor(...) sandbox escape. Instead, the attacker can directly use the injected Playwright browser object to reach browser.browserType().launch(...) and spawn an arbitrary executable on the probe host/container.

This appears to be a separate issue from the previously published node:vm(GHSA-h343-gg57-2q67) breakout advisory because the root cause here is exposure of a dangerous host capability object to untrusted code, not prototype-chain access to process.

Details

A normal project member can create or edit monitors and monitor tests:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Common/Models/DatabaseModels/Monitor.ts#L45-L78 - https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Common/Models/DatabaseModels/MonitorTest.ts#L27-L60

The dashboard exposes a Playwright code editor for Synthetic Monitors and allows the user to queue a test run:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/App/FeatureSet/Dashboard/src/Components/Form/Monitor/MonitorStep.tsx#L861-L918 - https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/App/FeatureSet/Dashboard/src/Components/Form/Monitor/MonitorTest.tsx#L66-L84

The probe worker polls queued monitor tests and executes them:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Probe/Jobs/Monitor/FetchMonitorTest.ts#L55-L85

For MonitorType.SyntheticMonitor, the user-controlled customCode is passed into SyntheticMonitor.execute(...):

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Probe/Utils/Monitors/Monitor.ts#L323-L338

SyntheticMonitor.execute(...) then runs that code through VMRunner.runCodeInNodeVM(...) and injects the live Playwright browser and page objects into the VM context:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Probe/Utils/Monitors/MonitorTypes/SyntheticMonitor.ts#L156-L168

VMRunner.runCodeInNodeVM(...) creates a Node vm context and exposes host objects into it, including the additional context objects:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Common/Server/Utils/VM/VMRunner.ts#L323-L405

The proxy wrapper blocks only a small set of property names and still forwards normal method calls with the real host this binding. Because of that, untrusted monitor code can still use legitimate Playwright methods on the injected browser object.

That is enough for code execution because Playwright's Browser exposes browserType(), and BrowserType.launch() accepts attacker-controlled process launch options such as executablePath, args, and ignoreDefaultArgs. An attacker can therefore cause the probe to spawn an arbitrary executable. Even if Playwright later errors because the spawned process is not a real browser, the command has already executed.

This same execution path is also used for normal scheduled monitors, not only one-shot monitor tests:

- https://github.com/OneUptime/oneuptime/blob/8e90f451426b160718bdd1796b68c5ec15318101/Probe/Jobs/Monitor/FetchList.ts#L110-L121

As a result, the issue can be abused either as a one-shot RCE via Test Monitor or as a persistent scheduled RCE by saving a malicious Synthetic Monitor.

PoC

1. Log in as any user with normal project membership. 2. Go to Monitors -> Create New Monitor. 3. Select Synthetic Monitor. 4. In Playwright Code, paste the following script:

javascript const HostFunction = Object.getOwnPropertyDescriptor(console, "log").value.constructor;

return { data: { node: HostFunction('return process.version')(), cwd: HostFunction('return process.cwd()')(), id: HostFunction( 'return process.getBuiltinModule("childprocess").execSync("id").toString()' )(), }, };

5. Select any one browser type, for example Chromium. 6. Select any one screen type, for example Desktop. 7. Set retry count to 0. 8. Click Test Monitor and choose a probe.

Expected result:

- the monitor execution succeeded and in the Show More Details the command output is shown. <img width="899" height="249" alt="image" src="https://github.com/user-attachments/assets/98ebd26f-431b-438e-9459-7deeebf97b18" />

Impact

This is a server-side Remote Code Execution issue affecting the probe component.

Who is impacted:

- any OneUptime deployment where an attacker can obtain ordinary project membership - environments where the probe has access to internal services, secrets, Kubernetes metadata, database credentials, proxy credentials, or other cluster-local trust relationships

— GitHub