webpack-dev-server users' source code may be stolen when they access a malicious web site

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-2025-30359: 0.60% estimated exploitation activity in the next 30 days; percentile 48.67 (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.

Summary Source code may be stolen when you access a malicious web site. Details Because the request for classic script by a script tag is not subject to same origin policy, an attacker can inject <script src="http://localhost:8080/main.js" in their site and run the script. Note that the attacker has to know the port and the output entrypoint script path. Combined with prototype pollution, the attacker can get a reference to the webpack runtime variables. By using Function::toString against the values in webpackmodules, the attacker can get the source code. PoC 1. Download reproduction.zip and extract it 2. Run npm i 3. Run npx webpack-dev-server 4. Open https://e29c9a88-a242-4fb4-9e64-b24c9d29b35b.pages.dev/ 5. You can see the source code output in the document and the devtools console. The script in the POC site is: This script uses the function generated by renderRequire. Especially, it uses the fact that Array::forEach is called for webpackrequire.i and execOptions contains…

Published by the source

4 Jun 2025, 21:09 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:38 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-4v9v-hfq4-rm2v

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-4v9v-hfq4-rm2v

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# Patch Next advisory brief: CVE-2025-30359

Advisory: webpack-dev-server users' source code may be stolen when they access a malicious web site
IDs: CVE-2025-30359, GHSA-4v9v-hfq4-rm2v
Record: https://patchnext.com/advisories/cve-2025-30359 (revision 2, source checked 26 Oct 2026, 12:38 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 5.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm webpack-dev-server: affected <= 5.2.0; fixed in 5.2.1

## 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-4v9v-hfq4-rm2v (OSV record GHSA-4v9v-hfq4-rm2v lists affected ranges: npm webpack-dev-server >=0 <5.2.1 (fixed))
- Verified: https://github.com/advisories/GHSA-4v9v-hfq4-rm2v (GitHub-reviewed advisory GHSA-4v9v-hfq4-rm2v lists affected ranges: npm webpack-dev-server >=0 <=5.2.0)

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