CVE-2026-39363 — vite
Fix: vitejs/vite#22159CVE-2026-39363 is a Information Exposure vulnerability in vite. 1 public exploit reference exists, so weaponization risk is real. A fix is available for vite — see the affected versions and patch details below.
Vite Affected by Arbitrary File Read via Vite Dev Server WebSocket
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.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39363.
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.
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.
vitenpmDescription
Summary
server.fs check was not enforced to the fetchModule method that is exposed in Vite dev server's WebSocket.
Impact
Only apps that match the following conditions are affected:
- explicitly exposes the Vite dev server to the network (using
--hostorserver.hostconfig option) - WebSocket is not disabled by
server.ws: false
Arbitrary files on the server (development machine, CI environment, container, etc.) can be exposed.
Details
If it is possible to connect to the Vite dev server’s WebSocket without an Origin header, an attacker can invoke fetchModule via the custom WebSocket event vite:invoke and combine file://... with ?raw (or ?inline) to retrieve the contents of arbitrary files on the server as a JavaScript string (e.g., export default "...").
The access control enforced in the HTTP request path (such as server.fs.allow) is not applied to this WebSocket-based execution path.
PoC
-
Start the dev server on the target Example (used during validation with this repository):
pnpm -C playground/alias exec vite --host 0.0.0.0 --port 5173 -
Confirm that access is blocked via the HTTP path (example: arbitrary file)
curl -i 'http://localhost:5173/@fs/etc/passwd?raw'Result:
403 Restricted(outside the allow list) <img width="3898" height="1014" alt="image" src="https://github.com/user-attachments/assets/f6593377-549c-45d7-b562-5c19833438af" /> -
Confirm that the same file can be retrieved via the WebSocket path By connecting to the HMR WebSocket without an
<img width="1049" height="296" alt="image" src="https://github.com/user-attachments/assets/af969f7b-d34e-4af4-8adb-5e2b83b31972" />Originheader and sending avite:invokerequest that callsfetchModulewith afile://...URL and?raw, the file contents are returned as a JavaScript module.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | vite | ≥ 8.0.0&&< 8.0.5 | 8.0.5npm install vite@8.0.5 |
| 📦npm | vite | ≥ 7.0.0&&< 7.3.2 | 7.3.2npm install vite@7.3.2 |
| 📦npm | vite | ≥ 6.0.0&&< 6.4.2 | 6.4.2npm install vite@6.4.2 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vite, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vite to 8.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39363 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-39363 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-39363. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.5 for RHEL 8 | automation-gateway-0:2.5.20260422-3.el8ap | RHSA-2026:24761 |
| Red Hat Ansible Automation Platform 2.6 for RHEL 9 | automation-platform-ui-0:2.6.9-1.el9ap | RHSA-2026:24762 |
| Red Hat Ansible Automation Platform 2.6 | ansible-automation-platform-tech-preview/mcp-server-rhel9:1779783248 | RHSA-2026:24866 |
| Red Hat Ansible Automation Platform 2.7 | ansible-automation-platform-27/gateway-rhel9:1787218409 | RHSA-2026:59153 |
Frequently Asked Questions
Is CVE-2026-39363 in your dependencies?
O3 Security finds CVE-2026-39363 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.