CVE-2026-6402: webpack-dev-server vulnerable to cross-origin source code exposure on non-HTTPS origins

Vulnerability summary

CVE-2026-6402 is a medium (CVSS 6.5) Exposed Dangerous Method or Function vulnerability in webpack-dev-server. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 21.7% of scored vulnerabilities.

Timeline

1. 12-05-2026
   PublishedVulnerability first disclosed.
2. 12-05-2026
   Last modifiedVulnerability information updated.

Description

webpack-dev-server versions up to and including 5.2.3 are vulnerable to cross-origin source code exposure when serving over a non-potentially trustworthy origin such as plain HTTP. The previous fix relied on the Sec-Fetch-Mode and Sec-Fetch-Site request headers, which browsers omit for non-trustworthy origins, allowing a malicious site to load the bundled source as a script and read it across origins. Impact: an attacker controlling a website visited by a developer running webpack-dev-server can recover the application source code when the dev server runs over HTTP at a guessable host and port. Chromium based browsers from Chrome 142 onward are not affected due to local network access restrictions. Upgrade to webpack-dev-server 5.2.4 or later, which sets Cross-Origin-Resource-Policy: same-origin on responses.

• CWE-749Exposed Dangerous Method or FunctionThe product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.