Glances: Cross-Origin Information Disclosure via Unauthenticated REST API (/api/4) due to Permissive CORS
Date: 2026-04
Affected: pip/Glances
Attack vector: info-disclosure
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-34839
CWE: CWE-200
CWE-306
CWE-942
CVSS: 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N)

### 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> ``` 2. Open the file in a browser whi


Mitigations:

Architectural layers (MAESTRO):