CVE-2026-34839 — glances

Summary

The Glances web server exposes a REST API (/api/4/*) that is accessible without authentication and allows cross-origin requests from any origin due to a permissive CORS policy (Access-Control-Allow-Origin: *).

This allows a malicious website to read sensitive system information from a running Glances instance in the victim’s browser, leading to cross-origin data exfiltration.

While a previous advisory exists for XML-RPC CORS issues, this report demonstrates that the REST API (/api/4/*) is also affected and exposes significantly more sensitive data.

Details

When Glances is started in web mode (e.g., glances -w -B 0.0.0.0), it exposes a REST API endpoint at: http://<host>:61208/api/4/all The server responds with: Access-Control-Allow-Origin: *

This allows any origin to perform cross-origin requests and read responses.

The /api/4/all endpoint returns extensive system information, including:

• Process list (processlist)
• System details (hostname, OS, CPU info)
• Memory and disk usage
• Network interfaces and IP address
• Running services and metrics Because no authentication is required by default, this data is accessible to any web page.

PoC

1. Start Glances: glances -w -B 0.0.0.0

2. Create a malicious HTML file:

<!DOCTYPE html>
<html>
<body>
<script>
fetch("http://<victim-ip>:61208/api/4/all")
  .then(r => r.json())
  .then(data => {
    console.log("DATA:", data);
  });
</script>
</body>
</html>

1. Open the file in a browser while Glances is running.
2. Observe that the browser successfully retrieves sensitive system information from the API. This works cross-origin (e.g., from file:// or attacker-controlled domains).

Impact

A remote attacker can host a malicious website that, when visited by a victim running Glances, can:

• Read sensitive system information
• Enumerate running processes
• Identify network configuration and IP addresses
• Fingerprint the host system

This requires no authentication and no user interaction beyond visiting a web page. This represents a cross-origin information disclosure vulnerability and can aid further attacks such as reconnaissance or targeted exploitation.