What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-12 · updated 2026-06-17
• Weakness: CWE-749

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.

Affected products

• webpack-dev-server: before 5.2.4 — fixed in 5.2.4
• Npm Webpack-Dev-Server: before 5.2.4 — fixed in 5.2.4

How to fix

Upgrade to a fixed version: webpack-dev-server 5.2.4; Npm Webpack-Dev-Server 5.2.4. Check the vendor advisory for mitigations.

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-79cf-xcqc-c78w

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