Code Injection in browserstack-runner (CVE-2026-49143)
Summary
Code injection in browserstack-runner (CVE-2026-49143). Successful exploitation can lead to full system takeover. Exploitable via context.
Original description
The description as published by the source.
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:
// lib/server.js lines 504-510
var context = { input: query.arguments, format: util.format, output: '' };
var tryEvalOrString = 'function (arg) { try { return eval(\'o = \' + arg); } catch (e) { return arg; } }';
vm.runInNewContext('output = format.apply(null, input.map(' + tryEvalOrString + '));', context);
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
# Terminal 1: start the runner
echo 't' > t.html
echo '{"username":"X","key":"X","test_path":"t.html","test_framework":"qunit","browsers":[]}' > browserstack.json
node bin/runner.js
# Terminal 2: exploi…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-49143 has been found in browserstack-runner.
Attackers can target a specific entry point like context over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 8.8/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "browserstack-runner CVE-2026-49143" on the vendor's site.
CVE-2026-49143 (browserstack-runner) — CWE-94 / CVSS v3 8.8
Attack vector: adjacent-network / unauthenticated / no user interaction
Attack surface: context / util.format / _progress / _report
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Arbitrary code execution (CWE-94) exists in browserstack-runner. Attackers reach the vulnerable code path via context without authentication.
Check the vendor advisory for the affected versions of browserstack-runner. Attack surface: context / util.format / _progress / _report.
Severity: High (CVSS 8.8/10). Successful exploitation can lead to full system takeover.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'browserstack-runner' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'browserstack-runner' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
browserstack-runnerを grep し、稼働しているサービス・バージョンを把握する。 -
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web disclosure@vulncheck.com
- web github.com