Which versions of Vite are affected by CVE-2026-39363?

Vite dev server versions prior to 6.4.2, 7.3.2, or 8.0.5 contain a critical WebSocket vulnerability that allows unauthenticated attackers to read arbitrary files-including credentials, source code,…. A patch is available.

Is there a public PoC exploit available for CVE-2026-39363?

Yes, a public proof-of-concept exploit is available for CVE-2026-39363. Prioritise patching immediately. EPSS: 0.1%.

How to fix or mitigate CVE-2026-39363?

Within 24 hours: Audit all Vite dev server deployments to identify instances running versions before 6.4.2, 7.3.2, or 8.0.5, and document exposure scope (internal networks, public exposure via --host). Within 7 days: Upgrade all affected Vite instances to 6.4.2, 7.3.2, or 8.0.5 (select version matching current minor release). Within 30 days: Review and remediate any credentials or secrets potentially exposed through dev server access; rotate credentials accessed from affected development and CI environments; implement network isolation for dev servers and disable --host flag unless strictly required with Origin header validation.

Vite CVE-2026-39363

Q: What is the CVSS score of CVE-2026-39363?

CVE-2026-39363 has a CVSS 4.0 base score of 8.2 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.1%.

HIGH

Information Exposure (CWE-200)

2026-04-06 https://github.com/vitejs/vite

GHSA-p9ff-h696-f583

Information Disclosure

8.2

CVSS 4.0 · Vendor: https://github.com/vitejs/vite

Severity by source

Vendor (https://github.com/vitejs/vite) PRIMARY

8.2 HIGH

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Red Hat

7.5 HIGH

qualitative

Primary rating from Vendor (https://github.com/vitejs/vite).

CVSS VectorVendor: https://github.com/vitejs/vite

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Re-analysis Queued

Apr 15, 2026 - 20:22 vuln.today

cvss_changed

Analysis Generated

Apr 07, 2026 - 00:15 vuln.today

Patch released

Apr 07, 2026 - 00:15 nvd

Patch available

CVE Published

Apr 06, 2026 - 18:03 nvd

HIGH 8.2

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

34 npm packages depend on vite (30 direct, 4 indirect)

Ecosystem-wide dependent count for version 8.0.0.

DescriptionCVE.org

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 --host or server.host config 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):

bash

   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)

bash

   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 Origin header and sending a vite:invoke request that calls fetchModule with a file://... URL and ?raw, the file contents are returned as a JavaScript module. <img width="1049" height="296" alt="image" src="https://github.com/user-attachments/assets/af969f7b-d34e-4af4-8adb-5e2b83b31972" /> <img width="1382" height="955" alt="image" src="https://github.com/user-attachments/assets/6a230d2e-197a-4c9c-b373-d0129756d5d7" />

AnalysisAI

Vite dev server WebSocket allows unauthorized file system access, bypassing server.fs.allow restrictions when developers expose dev servers to networks (via --host). Attackers exploiting this can read arbitrary files (credentials, source code, secrets) from the development machine or CI environment through a WebSocket vite:invoke event calling fetchModule with file:// URLs. Vendor-released patches available in versions 6.4.2, 7.3.2, and 8.0.5. Public exploit code exists with detailed proof-of-concept demonstrating /etc/passwd retrieval via WebSocket without Origin header validation.

Technical ContextAI

Vite is a modern JavaScript build tool and development server (pkg:npm/vite) that provides Hot Module Replacement (HMR) functionality over WebSocket connections. The vulnerability stems from an access control inconsistency mapped to CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). While HTTP-based file access correctly enforces server.fs.allow and server.fs.strict configuration to prevent path traversal outside designated directories, the WebSocket event handler for vite:invoke exposes a fetchModule method that bypasses these checks entirely. The WebSocket transport lacks Origin header validation in affected configurations, and the file:// protocol handler combined with query parameters (?raw or ?inline) transforms arbitrary filesystem content into JavaScript module exports. This architectural flaw creates two distinct execution paths with divergent security controls: HTTP requests properly validate filesystem boundaries, while WebSocket RPC calls to internal methods do not inherit these restrictions.

RemediationAI

Immediately upgrade to patched Vite versions: 6.4.2 or later for the 6.x branch, 7.3.2 or later for the 7.x branch, or 8.0.5 or later for the 8.x branch as documented in GitHub releases at github.com/vitejs/vite/releases. The fix is implemented in commit f02d9fde0b195afe3ea2944414186962fbbe41e0 and pull request #22159 available at github.com/vitejs/vite/pull/22159. For environments where immediate patching is not feasible, implement the following workarounds: restrict dev server binding to localhost only by removing --host flags and avoiding server.host configuration, or disable WebSocket functionality entirely by setting server.ws: false in Vite configuration (note this breaks HMR features). In CI/CD environments, ensure dev servers are isolated within containers without external network exposure and never expose development servers directly to untrusted networks. Review access logs for WebSocket connections with vite:invoke events targeting file:// URLs as potential indicators of exploitation attempts. Complete security advisory and patch details are available at github.com/vitejs/vite/security/advisories/GHSA-p9ff-h696-f583.