CVE-2026-9595
Description
A flaw was found in webpack-dev-server. When a user configures a proxy with a broad context, such as '/', and enables WebSocket (ws: true) forwarding, the development server's own Hot Module Replacement (HMR) WebSocket can be intercepted. This interception leads to the leakage of the browser's cookies and Origin header to the proxy target, bypassing the server's Host/Origin validation. Additionally, it can corrupt the HMR socket, resulting in a denial of service for the HMR functionality.
Statement
This vulnerability is rated as having an Important impact because improper handling of broad proxy routes allows sensitive browser data, including session tokens and origin metadata, to be exfiltrated to backend targets while circumventing server origin checks. In Red Hat environments, webpack-dev-server is primarily utilized in development workflows, frontend build pipelines, and containerized development tooling rather than production service delivery. However, when local or containerized development servers are configured with overly permissive proxy rules, remote attackers can compromise session integrity and trigger denial-of-service conditions during development sessions.
Mitigation
To mitigate this issue, users should avoid configuring `webpack-dev-server` with a broad proxy context (e.g., `/`) when WebSocket forwarding (`ws: true`) is enabled. Instead, define specific paths for the proxy context. Alternatively, disable WebSocket forwarding by omitting `ws: true` from the proxy entry if WebSocket functionality is not required for the proxy target. This configuration change may require restarting the `webpack-dev-server` instance to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.1 | 4.3 | 5.3 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | Low | None |
| User Interaction | Required | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | Low | Low | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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