browserstack-runner vulnerable to Remote Code Execution via vm sandbox escape in _log HTTP handler

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-49143: 0.80% estimated exploitation activity in the next 30 days; percentile 56.72 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The HTTP handler /log in lib/server.js (lines 491–515) of browserstack-runner passes unauthenticated user-supplied data to vm.runInNewContext() combined with eval(), enabling a sandbox escape and arbitrary code execution on the host system. Details When browserstack-runner starts, it creates an HTTP server on port 8888 (configurable) that listens on all network interfaces (0.0.0.0). The /log endpoint accepts POST requests and processes the JSON body as follows: The vm module is not a security mechanism per Node.js documentation. The context object contains a reference to util.format (a host-context Function), enabling sandbox escape via this.constructor.constructor("return process")(). Unlike the progress and report handlers which verify worker UUID authentication, the log handler does not gate on authentication. Proof of Concept Impact An attacker on the same network as a developer running browserstack-runner can execute arbitrary commands on the developer's machine without…

Published by the source

3 Jun 2026, 21:39 UTC

Last modified by the source

3 Jun 2026, 21:56 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6vr3-7wcx-v5g5

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-6vr3-7wcx-v5g5

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-49143

Advisory: browserstack-runner vulnerable to Remote Code Execution via vm sandbox escape in _log HTTP handler
IDs: CVE-2026-49143, GHSA-6vr3-7wcx-v5g5
Record: https://patchnext.com/advisories/cve-2026-49143 (revision 3, source checked 26 Oct 2026, 12:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm browserstack-runner: affected <= 0.9.5

## Suggested inspection (read-only)
- `npm ls browserstack-runner --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on browserstack-runner.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-6vr3-7wcx-v5g5 (OSV record GHSA-6vr3-7wcx-v5g5 lists affected ranges: npm browserstack-runner >=0 <=0.9.5)
- Verified: https://github.com/advisories/GHSA-6vr3-7wcx-v5g5 (GitHub-reviewed advisory GHSA-6vr3-7wcx-v5g5 lists affected ranges: npm browserstack-runner >=0 <=0.9.5)

Commands are suggestions: review each one before running it.