CVE-2026-53633 is a critical-severity (CVSS 9.8) CWE-749 vulnerability in @vitest/browser. O3 Security confirms whether CVE-2026-53633 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Vitest: Exposed Browser Mode API Can Proxy CDP and Overwrite Config Files, Leading to RCE
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53633.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-53633 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 366,357 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@vitest/browsernpmDescription
Vitest is a testing framework powered by Vite. From 3.0.0 until 3.2.5, 4.1.8, and 5.0.0-beta.4, Vitest Browser Mode exposed a cdp() API that forwarded raw Chrome DevTools Protocol methods without being gated by allowWrite or allowExec, allowing a remote client with exposed browser API metadata to use CDP Page.setDownloadBehavior and Runtime.evaluate to overwrite vite.config.ts and execute attacker-controlled Node.js code. This issue is fixed in versions 3.2.5, 4.1.8, and 5.0.0-beta.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @vitest/browser | ≥ 5.0.0-beta.0&&< 5.0.0-beta.4 | 5.0.0-beta.4 |
| 📦npm | @vitest/browser | ≥ 4.0.0&&< 4.1.8 | 4.1.8 |
| 📦npm | @vitest/browser | ≥ 3.0.0&&< 3.2.5 | 3.2.5 |
| 📦npm | vite-plus | all versions | 0.1.24 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @vitest/browser. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @vitest/browser to 5.0.0-beta.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53633 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-53633 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-53633. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-53633 in your dependencies?
O3 detects CVE-2026-53633 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.