CVE-2026-34839: Glances Vulnerable to Cross-Origin Information Disclosure via Unauthenticated REST API (/api/4) due to Permissive CORS
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 while Glances is running. 3. 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.
Other sources
Glances is an open-source system cross-platform monitoring tool. Prior to version 4.5.4, 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. Version 4.5.4 patches the issue.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-34839?
CVE-2026-34839 has been rated as a moderate severity vulnerability due to its potential for information disclosure.
How do I fix CVE-2026-34839?
To fix CVE-2026-34839, upgrade Glances to version 4.5.4 or later to mitigate the vulnerability.
What is the impact of CVE-2026-34839?
CVE-2026-34839 allows unauthenticated users to access sensitive data through the REST API due to permissive CORS settings.
Which versions of Glances are affected by CVE-2026-34839?
CVE-2026-34839 affects all versions of Glances prior to 4.5.4.
Is authentication required to exploit CVE-2026-34839?
No, CVE-2026-34839 can be exploited without any authentication, making it more dangerous.