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

> Unauthenticated attackers can execute arbitrary code on systems running BrowserStack Runner by sending crafted JSON payloads to the /_log handler.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Jun 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-6vr3-7wcx-v5g5

## What is CVE-2026-49143?

CVE-2026-49143 is a high-severity code injection vulnerability in browserstack-runner, published on 2 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-49143?

2 open source packages ship an affected version, including browserstack-runner.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `browserstack-runner` | npm | All versions to 0.9.5 | None |
| `browserstack-runner` | npm | All versions to 0.9.5 | None |

## How do I fix CVE-2026-49143?

No fix has been published for CVE-2026-49143 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-49143 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49143 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49143 and fix it if it is affected.

What it is: CVE-2026-49143 is a high-severity code injection vulnerability in browserstack-runner, published on 2 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49143 exists.

Affected packages and fixed versions:
- browserstack-runner (npm): affected all versions up to 0.9.5; no fix listed
- browserstack-runner (npm): affected all versions up to 0.9.5; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49143/ (Markdown: https://insights.sbomify.com/CVE-2026-49143/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49143
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49143
- OSV: https://osv.dev/vulnerability/CVE-2026-49143

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49143/
Summaries are generated and may contain mistakes; the official description above is the record.