[原创] 某设备CoAP协议漏洞挖掘实战-智能设备-看雪-安全社区|安全招聘|kanxue.com

[原创] 某设备CoAP协议漏洞挖掘实战

发表于: 2022-8-9 21:13 20842

[原创] 某设备CoAP协议漏洞挖掘实战

风亦映寒

2022-8-9 21:13

20842

发现看雪等国内安全论坛好像CoAP协议相关内容很少，以及CVE中基本也是CoAP协议库存在的漏洞，所以将最近对某设备CoAP漏洞挖掘的相关分析写一下。

CoAP可以简单的当做基于UDP协议的轻量化HTTP协议。

协议栈：

Constrained RESTful Environments (CoRE)

CoAP Resource Discovery 机制

例: CoAP server 提供了2个资源

安全机制

CoAP 有四种安全机制： NoSec， PreSharedKey ，RawPublicKey，Certificate, 但是只有NoSec和RawPublicKey是强制实现的。

CoAP 本身没有实现认证和授权机制，而是通过 communication security（IPsec，DTLS）和object security 来完成。

安全考虑

CoAP协议默认端口为5683或5684，端口为5683时的安全机制为NoSec， 5684则是开启了DTLS。看了下设备端口开启的5683。

如下，设备实现了基于CoRE 的 Well-Known URI

所以可以直接进行 Resourse Discovery 过程：

可以看到，CoAPserver 提供了以下资源

逆向对应二进制看到的代码实现，对应的函数名和URI也可以推测下对应功能。

剩下的就是对这些函数进行进一步漏洞挖掘了。

挖掘成果：

coapsync_handler函数会将设备SSID，Pwd等参数返回给client，导致了信息泄露，比较鸡肋的一个洞。

Url字段数据导致的命令注入。

recv_cmdfile_handler会调用到cmdupgrade_parse。

最终会调用函数do_upgrade, 而Url字段数据会拼接到system执行的命令中，达成未授权RCE.

cotopaxi

https://github.com/Samsung/cotopaxi

libcoap，aiocoap等 coap 协议实现库

判断是否可以进行resource discovry 操作获取CoAP server 的资源

判断安全机制是哪种

判断是否实现了认证机制

对请求解析函数进行逆向分析

https://tools.ietf.org/html/rfc8615

https://datatracker.ietf.org/doc/html/rfc6690

https://en.wikipedia.org/wiki/Constrained_Application_Protocol

https://datatracker.ietf.org/doc/html/rfc7252

https://datatracker.ietf.org/doc/html/rfc5785

REQ: GET coap://server:port/.well-known/core
 
RES: 

  2.05 Content

  </sensors/temp>;if="sensor",

  </sensors/light>;if="sensor"

REQ: GET coap://server:port/.well-known/core

RES:

2.05 Content

</sensors/temp>;if="sensor",

</sensors/light>;if="sensor"

udp 0 0 0.0.0.0:5683 0.0.0.0:*

if ( *((_BYTE *)v21->hdr + 1) == 1 && !memcmp(key, &unk_A0DC, 4u) )
{

  coap_log_impl(7, "create default response for %s\n", ".well-known/core");

  v22 = wellknown_response(context, node->pdu);
}

if ( *((_BYTE *)v21->hdr + 1) == 1 && !memcmp(key, &unk_A0DC, 4u) )

{

coap_log_impl(7, "create default response for %s\n", ".well-known/core");

v22 = wellknown_response(context, node->pdu);

}

import asyncio

from aiocoap import *
 
async def main():

    protocol = await Context.create_client_context()

    msg = Message(code=GET, uri="coap://192.168.1.1:5683/.well-known/core")

    response = await protocol.request(msg).response

    print(response.payload)
 
asyncio.run(main())

import asyncio

from aiocoap import *

async def main():

protocol = await Context.create_client_context()

msg = Message(code=GET, uri="coap://192.168.1.1:5683/.well-known/core")

response = await protocol.request(msg).response

print(response.payload)

asyncio.run(main())

b'</>;title="General Info";ct=0,
...

</device/inform/boot>;title=device/inform/boot,</device/inform/syncreq>;title=device/inform/syncreq,</device/inform/off>;title=device/inform/off,</device/inform/hb>;title=device/inform/hb,</device/inform/data>;title=device/inform/data,

</device/cmd/file>;title=device/cmd/file

</async>;ct=0'

b'</>;title="General Info";ct=0,

...

</device/inform/boot>;title=device/inform/boot,</device/inform/syncreq>;title=device/inform/syncreq,</device/inform/off>;title=device/inform/off,</device/inform/hb>;title=device/inform/hb,</device/inform/data>;title=device/inform/data,

</device/cmd/file>;title=device/cmd/file

</async>;ct=0'

void *__fastcall start_coap_server_thread(void *a1)
{

 pthread_t v1; // $v0

 v1 = pthread_self();

 pthread_detach(v1);

 ...

 registerCoapMethod("device/inform/boot", coapboot_handler) 

 registerCoapMethod("device/inform/syncreq", coapsync_handler) 

 registerCoapMethod("device/inform/off", coapoff_handler) 

 registerCoapMethod("device/inform/hb", coaphb_handler )

 registerCoapMethod("device/inform/data", coapdata_handler) 

 registerCoadMethod("device/cmd/url", coapdata_url_handler)

 ...

 startCoapService("0.0.0.0", 5683);

 return 0;
}

void *__fastcall start_coap_server_thread(void *a1)

{

pthread_t v1; // $v0

v1 = pthread_self();

pthread_detach(v1);

...

registerCoapMethod("device/inform/boot", coapboot_handler)

registerCoapMethod("device/inform/syncreq", coapsync_handler)

registerCoapMethod("device/inform/off", coapoff_handler)

registerCoapMethod("device/inform/hb", coaphb_handler )

registerCoapMethod("device/inform/data", coapdata_handler)

registerCoadMethod("device/cmd/url", coapdata_url_handler)

...

startCoapService("0.0.0.0", 5683);

return 0;

}

...

cJSON_AddItemToObject(v73, "SSID", v13);

v14 = cJSON_CreateString(&v83[136]);

cJSON_AddItemToObject(v73, "SecurityMode", v14);

v15 = cJSON_CreateString(&v83[72]);

cJSON_AddItemToObject(v73, "Pwd", v15);
...