Webpack is a module bundler. From version 5.49.0 to before 5.104.0, when experiments.buildHttp is enabled, webpack’s HTTP(S) resolver (HttpUriPlugin) enforces allowedUris only for the initial URL, but does not re-validate allowedUris after following HTTP 30x redirects. As a result, an import that appears restricted to a trusted allow-list can be redirected to HTTP(S) URLs outside the allow-list. This is a policy/allow-list bypass that enables build-time SSRF behavior (requests from the build machine to internal-only endpoints, depending on network access) and untrusted content inclusion in build outputs (redirected content is treated as module source and bundled). This issue has been patched in version 5.104.0.