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Medium, CVSS 5.3amended

webpack-dev-server vulnerable to cross-origin source code exposure on non-HTTPS origins

CVE-2026-6402GHSA-79cf-xcqc-c78w

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (webpack-dev-server 5.2.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
EPSS
  • CVE-2026-6402: 0.29% estimated exploitation activity in the next 30 days; percentile 21.77 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact When webpack-dev-server is running on a non-HTTPS origin (the default), cross-origin requests from malicious websites can load the dev server's JavaScript bundles via <script tags. The fix introduced in v5.2.1 (CVE-2025-30359) relied on Sec-Fetch-Mode and Sec-Fetch-Site request headers to block these requests, but browsers only send these headers for potentially trustworthy origins. Over plain HTTP, the headers are absent and the check is bypassed. An attacker who knows the dev server's host, port, and output path can exfiltrate all module source code by intercepting the webpack runtime's module registration. This does not affect Chrome 142+ (and other Chromium-based browsers) due to local network access restrictions. Patches Patched in webpack-dev-server = 5.2.4 by setting Cross-Origin-Resource-Policy: same-origin on responses. Workarounds Run the dev server with HTTPS enabled (--https or server.type: 'https' in config). Resources - GHSA-4v9v-hfq4-rm2v (CVE-2025-30359) -…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-79cf-xcqc-c78w

  2. Revision 1 · created ·

    Published from osv record GHSA-79cf-xcqc-c78w

Agent brief

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# Patch Next advisory brief: CVE-2026-6402

Advisory: webpack-dev-server vulnerable to cross-origin source code exposure on non-HTTPS origins
IDs: CVE-2026-6402, GHSA-79cf-xcqc-c78w
Record: https://patchnext.com/advisories/cve-2026-6402 (revision 2, source checked 26 Oct 2026, 12:52 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 5.2.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm webpack-dev-server: affected <= 5.2.3; fixed in 5.2.4

## 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-79cf-xcqc-c78w (OSV record GHSA-79cf-xcqc-c78w lists affected ranges: npm webpack-dev-server >=0 <5.2.4 (fixed))
- Verified: https://github.com/advisories/GHSA-79cf-xcqc-c78w (GitHub-reviewed advisory GHSA-79cf-xcqc-c78w lists affected ranges: npm webpack-dev-server >=0 <=5.2.3)

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