Impact
When webpack-dev-server is running on a non-HTTPS origin (the default), cross-origin requests from malicious websites can load the dev server's JavaScript bundles via <script> tags. The fix introduced in v5.2.1 (CVE-2025-30359) relied on Sec-Fetch-Mode and Sec-Fetch-Site request headers to block these requests, but browsers only send these headers for potentially trustworthy origins. Over plain HTTP, the headers are absent and the check is bypassed.
An attacker who knows the dev server's host, port, and output path can exfiltrate all module source code by intercepting the webpack runtime's module registration.
This does not affect Chrome 142+ (and other Chromium-based browsers) due to local network access restrictions.
Patches
Patched in webpack-dev-server >= 5.2.4 by setting Cross-Origin-Resource-Policy: same-origin on responses.
Workarounds
Run the dev server with HTTPS enabled (--https or server.type: 'https' in config).
References
sapphi-red Reporter
UlisesGascon Remediation developer
bjohansebas Remediation developer
alexander-akait Remediation reviewer
Impact
When webpack-dev-server is running on a non-HTTPS origin (the default), cross-origin requests from malicious websites can load the dev server's JavaScript bundles via
<script>tags. The fix introduced in v5.2.1 (CVE-2025-30359) relied onSec-Fetch-ModeandSec-Fetch-Siterequest headers to block these requests, but browsers only send these headers for potentially trustworthy origins. Over plain HTTP, the headers are absent and the check is bypassed.An attacker who knows the dev server's host, port, and output path can exfiltrate all module source code by intercepting the webpack runtime's module registration.
This does not affect Chrome 142+ (and other Chromium-based browsers) due to local network access restrictions.
Patches
Patched in webpack-dev-server >= 5.2.4 by setting
Cross-Origin-Resource-Policy: same-originon responses.Workarounds
Run the dev server with HTTPS enabled (
--httpsorserver.type: 'https'in config).References