webpack-dev-server vulnerable to denial of service via a malformed Host or Origin header

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS

• CVE-2026-14631: 0.52% estimated exploitation activity in the next 30 days; percentile 44.02 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact An unauthenticated peer that can reach the webpack-dev-server process can terminate it by sending either a normal HTTP request with a malformed Host header, or a WebSocket upgrade to the default /ws endpoint with a malformed Origin header. The malformed header triggers an uncaught exception in the host-validation path and crashes the dev server process. Patches Fixed in webpack-dev-server 5.2.6 by treating malformed Host and Origin header values as invalid rather than throwing (see PR #5699). Workarounds Keep the dev server bound to localhost (the default) and do not expose it to untrusted networks.

Published by the source

20 Jul 2026, 22:02 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:57 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m28w-2pqf-7qgj

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m28w-2pqf-7qgj

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# Patch Next advisory brief: CVE-2026-14631

Advisory: webpack-dev-server vulnerable to denial of service via a malformed Host or Origin header
IDs: CVE-2026-14631, GHSA-m28w-2pqf-7qgj
Record: https://patchnext.com/advisories/cve-2026-14631 (revision 2, source checked 26 Oct 2026, 12:57 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: webpack-dev-server 5.2.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm webpack-dev-server: affected <= 5.2.5; fixed in 5.2.6

## Suggested inspection (read-only)
- `npm ls webpack-dev-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on webpack-dev-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m28w-2pqf-7qgj (OSV record GHSA-m28w-2pqf-7qgj lists affected ranges: npm webpack-dev-server >=0 <5.2.6 (fixed))
- Verified: https://github.com/advisories/GHSA-m28w-2pqf-7qgj (GitHub-reviewed advisory GHSA-m28w-2pqf-7qgj lists affected ranges: npm webpack-dev-server >=0 <=5.2.5)

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