CVE-2025-30359: webpack-dev-server users' source code may be stolen when they access a malicious web site

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2025-06-03 · updated 2026-06-17
Weakness: CWE-749

Description

webpack-dev-server allows users to use webpack with a development server that provides live reloading. Prior to version 5.2.1, webpack-dev-server users' source code may be stolen when they access a malicious web site. Because the request for classic script by a script tag is not subject to same origin policy, an attacker can inject a malicious script 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 `__webpack_modules__`, the attacker can get the source code. Version 5.2.1 contains a patch for the issue.

Affected products

webpack-dev-server: before 5.2.1 — fixed in 5.2.1
Npm Webpack-Dev-Server: before 5.2.1 — fixed in 5.2.1

How to fix

Upgrade to a fixed version: webpack-dev-server 5.2.1; Npm Webpack-Dev-Server 5.2.1. Check the vendor advisory for mitigations.

References

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