GHSA-w856-8p3r-p338 Glances: XML-RPC Server Missing Host Header Validation Enables DNS Rebinding Attack
SummaryThe Glances XML-RPC server (`glances -s`, implemented in `glances/server.py`) does not validate the HTTP `Host` header, leaving it vulnerable to DNS rebinding attacks.  CVE-2026-32632 (patched in 4.5.2) added `TrustedHostMiddleware` to the REST/WebUI server; the MCP server has had equivalent protection since 4.5.1. The XML-RPC server received neither fix and has no `allowed-hosts` configuration key.  Combined with the unrestricted `Access-Control-Allow-Origin: *` header (see companion advisory for CVE-2026-33533 and its incomplete fix), an attacker can exploit DNS rebinding to exfiltrate the full system monitoring dataset from a victim's browser.Details**Affected component:** `glances/server.py` — `GlancesXMLRPCHandler` / `GlancesXMLRPCServer`**Direct URL (commit 04579778e733d705898a169e049dc84772c852da):**https://github.com/nicolargo/glances/blob/04579778e733d705898a169e049dc84772c852da/glances/server.pyContrast — patched backends:https://github.com/nicolargo/glances/blob/04579778e733d705898a169e049dc84772c852da/glances/outputs/glances_restful_api.pyhttps://github.com/nicolargo/glances/blob/04579778e733d705898a169e049dc84772c852da/glances/outputs/glances_mcp.pyThe `GlancesXMLRPCHandler` class inherits from Python's `xmlrpc.server.SimpleXMLRPCRequestHandler` and does not override `parse_request()` to inspect or validate the `Host` header.Contrast this with the two other Glances server backends, both of which received host-validation hardening:**REST / WebUI server** (`glances/outputs/glances_restful_api.py`) — patched in 4.5.2:**MCP server** (`glances/outputs/glances_mcp.py`) — protected since 4.5.1:**XML-RPC server** (`glances/server.py`) — no equivalent exists: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:| Server type | Host header          | HTTP status | Data returned |
|-------------|----------------------|-------------|---------------|
| XML-RPC     | `attacker.example.com` | 200 OK    | Yes — VULNERABLE |
| XML-RPC     | `127.0.0.1:61209`    | 200 OK      | Yes (baseline)   |
| REST API    | `attacker.example.com` | 400 Bad Request | No — patched |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****Step 2 — Confirm the server accepts an arbitrary Host header**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)****Step 4 — Full DNS rebinding exploitation (real-world path)**Attacker registers `attacker.example.com` with a low-TTL (1 second) DNS record initially pointing to their own server IP.Attacker serves the following page from `http://attacker.example.com`:Victim visits `http://attacker.example.com` in their browser.After TTL expiry, the attacker's DNS server responds with `127.0.0.1`.The browser's `fetch()` call is sent to `127.0.0.1:61209` with `Host: attacker.example.com`; the XML-RPC server accepts it.The `Access-Control-Allow-Origin: *` header (see companion advisory) allows the browser to read the response body.The attacker receives the complete system monitoring snapshot.Tools that simplify DNS rebinding for research/testing include:[Singularity](https://github.com/nccgroup/singularity)[rbndr.us](https://rbndr.us)**Step 5 — Confirm absence of Host check in source**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`: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 DisclosureThe 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.CreditsThis issue was identified by Michał Majchrowicz and Marcin Wyczechowski, members of the AFINE Team.
CVSS v3.1 score: 5.3