Headline
CVE-2021-21950: TALOS-2021-1378 || Cisco Talos Intelligence Group
An out-of-bounds write vulnerability exists in the CMD_DEVICE_GET_SERVER_LIST_REQUEST functionality of the home_security binary of Anker Eufy Homebase 2 2.1.6.9h in function recv_server_device_response_msg_process. A specially-crafted network packet can lead to code execution.
Summary
An out-of-bounds write vulnerability exists in the CMD_DEVICE_GET_SERVER_LIST_REQUEST functionality of the home_security binary of Anker Eufy Homebase 2 2.1.6.9h. A specially-crafted network packet can lead to code execution.
Tested Versions
Anker Eufy Homebase 2 2.1.6.9h
Product URLs
https://us.eufylife.com/products/t88411d1
CVSSv3 Score
10.0 - CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CWE
CWE-119 - Improper Restriction of Operations within the Bounds of a Memory Buffer
Details
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 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", // [1]
0xd : "CMD_DEVICE_GET_RSA_KEY_REQUEST", // [2]
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",
0xfa1 : "wifi_channel_update",
0x1388 : "CMD_SET_DEFINE_COMMAND_VALUE",
0x1770 : "CMD_SET_DEFINE_COMMAND_STRING"
}
While some of these opcode names look tantalizing, only the opcodes less than 0x10 require no authentication, so we’re limited to CMD_DEVICE_GET_SERVER_LIST_REQUEST [1] and CMD_DEVICE_GET_RSA_KEY_REQUEST [2]. For the purposes of this advisory, we only need one of these: CMD_DEVICE_GET_SERVER_LIST_REQUEST. Since the same vulnerable code pattern is found in two different functions, we’ll discuss them separately.
CVE-2021-21950 - recv_server_device_response_msg_process
In function recv_server_device_response_msg_process, the CMD_DEVICE_GET_SERVER_LIST_REQUEST request is parsed as shown below:
05a1748 uint32_t recv_server_device_response_msg_process(struct dev_packet* devpkt, int32_t inp_msglen, struct sockaddr* dstaddr, int32_t sockfd)
005a179c uint32_t opcode = zx.d((zx.d(devpkt->opcode:1.b) << 8).w | zx.w(devpkt->opcode.b))
005a17c8 struct dev_packet_full resp_buf
005a17c8 memset(&resp_buf, 0, 0x425)
005a17d8 uint32_t scratch = opcode
005a17e0 struct aes_key_st scratchbuf
005a17e0 if (scratch == 0xc)
005a1acc m_heart_timemout_nums = 0
005a1ad8 m_udp_server_connect = 1
005a1ae8 int32_t resp_time = 0
005a1b0c memcpy(&resp_buf, devpkt, inp_msglen)
005a1b30 struct cJSON* jsonobj = cJSON_Parse(&resp_buf.msg)
005a1b48 if (jsonobj != 0)
005a1b6c uint32_t udp_server_num = zx_Json_GetInt(jsonobj, "nums", 0) // [3]
005a1ba4 resp_time = zx_Json_GetInt(jsonobj, "utc_time", 0) // [4]
// [...]
005a1c84 s_udp_server_total_nums = udp_server_num
005a1e9c for (int32_t ctr = 0; ctr s< udp_server_num; ctr = ctr + 1)
005a1cb8 memset(&scratchbuf, 0, 0x80)
005a1cf8 sprintf(&scratchbuf, 0x79ca14, 0x79ca1c, ctr + 1, var_798, var_794, var_790, var_78c, var_788) {"%s%d"} {"domain"}
005a1d20 char* str_value = zx_Json_GetString(obj: jsonobj, string: &scratchbuf, output_ptr: nullptr) // [5]
005a1d38 if (str_value != 0 && strlen(str_value) u< 0x80)
005a1da0 memset((ctr << 7) + 0x88287c, 0, 0x80)
005a1e00 memcpy(0x88287c + (ctr << 7), str_value, strlen(str_value))
// [...]
005a1eb4 cJSON_Delete(cjson: jsonobj)
005a1ec0 int32_t var_768_4 = 0
005a1ed0 if (s_udp_server_total_nums s> 0)
005a1ed8 update_udp_push_config_file()
005a1ee8 scratch = send_device_packet_by_command_id(opcode: 0xd)
Utilizing the cJSON library to pull out the nums field [3], the utc_time field [4], and also a list of domains from the json of the server’s response [5], the CMD_DEVICE_GET_SERVER_LIST_REQUEST opcode then stores this server list information inside of the zx_udp_push_config.ini file. When valid, the file might look like so:
/~ cat /mnt/zx_udp_push_config.ini
[NET]
domain_total=3
current_index=2
app_server_domain=security-app.eufylife.com
domain1=p2p-vir-6.eufylife.com
domain2=p2p-vir-7.eufylife.com
domain3=mediaserver-usa3.eufylife.com
We now have enough context to discuss the vulnerability, so let us go back to a particular subset of the above recv_server_device_response_msg_process code:
005a1b48 if (jsonobj != 0)
005a1b6c uint32_t udp_server_num = zx_Json_GetInt(jsonobj, "nums", 0) // [6]
005a1ba4 resp_time = zx_Json_GetInt(jsonobj, "utc_time", 0)
// [...]
005a1c84 s_udp_server_total_nums = udp_server_num
005a1e9c for (int32_t ctr = 0; ctr s< udp_server_num; ctr = ctr + 1) // [7]
005a1cb8 memset(&scratchbuf, 0, 0x80)
005a1cf8 sprintf(&scratchbuf, 0x79ca14, 0x79ca1c, ctr + 1, var_798, var_794, var_790, var_78c, var_788) {"%s%d"} {"domain"}
005a1d20 char* str_value = zx_Json_GetString(obj: jsonobj, string: &scratchbuf, output_ptr: nullptr) // [8]
005a1d38 if (str_value != 0 && strlen(str_value) u< 0x80) // [9]
005a1da0 memset((ctr << 7) + 0x88287c, 0, 0x80) // [10]
005a1e00 memcpy(0x88287c + (ctr << 7), str_value, strlen(str_value)) // [11]
When pulling the nums field, which serves as the total number of UDP server domains, we must note the total lack of validation on this field anywhere thereafter [6]. Thus, the amount of iterations for the loop at [7] is entirely attacker-controlled, along with the int32_t ctr variable at [7] as well. If the search for domain1, domain2, … domain%d field from our packet JSON fails at [8], or if the string length of the value is greater than 0x80, we skip the branch at [9] but stay within our loop at [7]. The ctr variable keeps incrementing. With all this in mind we can reason that the lines at [10] and [11] can be hit with whatever value inside of ctr that an attacker chooses. While there is a total packet length limit of 0x425 bytes found much earlier in the codebase, there’s no requirement for our JSON to have domain1 and domain2 and so on and so forth. We would quickly run out of bytes before we could write outside of the char s_udp_server_list[0x80][8] at 0x88287c. Thus, simply by inserting something like "domain100000":aaaaaaaaaaaaaaa... and "nums":100001 into a CMD_DEVICE_GET_SERVER_LIST_REQUEST, one can write 0x80 bytes to 0x88287c + (100000 << 7), something applicable to any address in memory, resulting in a write-what-where and subsequent code execution.
Crash Information
Terminated with signal SIGSEGV, Segmentation fault.
#0 0x77226a84 in memset () from /lib/libc.so.0
[Current thread is 1 (LWP 5768)]
Backtrace stopped: frame did not save the PC
<(^.^)>#info reg
zero at v0 v1 a0 a1 a2 a3
R0 00000000 1100ff00 0216207c 0216207c 02162084 00000000 00000000 021620fc
t0 t1 t2 t3 t4 t5 t6 t7
R8 00000000 00000000 00000200 00000100 00000807 00000800 00000400 00000008
s0 s1 s2 s3 s4 s5 s6 s7
R16 6148b52a 7fe43468 00000036 771de280 7c6c0000 00000000 00000007 0000e436
t8 t9 k0 k1 gp sp s8 ra
R24 00000001 77226a30 00000000 00000000 0083bdb0 7c6fe498 00000000 005a1da8
sr lo hi bad cause pc
0100ff13 00000000 00000002 0216207c 0080000c 77226a84
fsr fir
00000000 00000000
<(^.^)>#x/4i $pc
=> 0x77226a84 <memset+84>: sw a1,-8(a0)
0x77226a88 <memset+88>: bne a0,a3,0x77226a80 <memset+80>
0x77226a8c <memset+92>: sw a1,-4(a0)
0x77226a90 <memset+96>: andi t0,a2,0x4
<(^.^)>#bt
#0 0x77226a84 in memset () from /lib/libc.so.0
#1 0x005a1da8 in recv_server_device_response_msg_process (p_data=0x7c6ff8ec, data_len=175, server_sin=0x7c6ff8d8, socket_id=22) at src/zx_push_interface.c:633
#2 0x005a6584 in process_msg (p_data=0x7c6ff8ec, data_len=175, server_sin=0x7c6ff8d8, socket_id=22) at src/zx_push_interface.c:1507
#3 0x005a108c in zx_push_recv_packet (socket_id=22) at src/zx_push_interface.c:462
#4 0x005a05b4 in init_udp_server_domain () at src/zx_push_interface.c:340
#5 0x005a1128 in zx_push_receiver_msg_process (argv=0x0) at src/zx_push_interface.c:473
#6 0x771c3264 in pthread_start_thread () from /lib/libpthread.so.0
#7 0x772007f8 in __thread_start () from /lib/libc.so.0
<(^.^)>#info reg a0
a0: 0x2162084
<(^.^)>#info proc map
Mapped address spaces:
Start Addr End Addr Size Offset objfile
0x400000 0x7f8000 0x3f8000 0x0 /bin/home_security
0x808000 0x837000 0x2f000 0x3f8000 /bin/home_security
CVE-2021-21951 - read_udp_push_config_file
The previously-mentioned bug is also found in a second function, read_udp_push_config_file, in the same code pattern. After reading the CMD_DEVICE_GET_SERVER_LIST_REQUEST in recv_server_device_response_msg_process, these values are then written into the /mnt/zx_udp_push_config.ini file. On reboot, read_udp_push_config_file is hit and we read the /mnt/zx_udp_push_config.ini config file, all the same vulnerability principles being applicable.
0059f2f4 if (zx_file_readcfg(file: "/mnt/zx_udp_push_config.ini", char *section: 0x79c980, headername: "domain_total", output: &var_110_0x80_size) != 0) {"[NET]"} // [1]
0059f348 $v0_1 = 0xffffffff
0059f324 else
0059f324 s_udp_server_total_nums = atoi(&var_110_0x80_size)
0059f334 if (s_udp_server_total_nums == 0)
0059f33c $v0_1 = 0xffffffff
0059f378 else
0059f378 memset(&var_110_0x80_size, 0, 0x80)
0059f3bc if (zx_file_readcfg(file: "/mnt/zx_udp_push_config.ini", char *section: 0x79c980, headername: "current_index", output: &var_110_0x80_size) != 0) {"[NET]"}
0059f400 $v0_1 = 0xffffffff
0059f3ec else
0059f3ec s_current_udp_server_index = atoi(&var_110_0x80_size)
0059f6bc while (true)
0059f6bc if (ctr s>= s_udp_server_total_nums) // [2]
0059f6bc if (s_udp_server_total_nums u>= s_current_udp_server_index && sx.d(*((s_current_udp_server_index << 7) + 0x88287c)) != 0)
0059f6e8 memset(0x8827f4, 0, 0x80)
0059f72c strncpy(0x8827f4, 0x88287c + (s_current_udp_server_index << 7), 0x7f) /
// [...]
0059f7a8 $v0_1 = 0
0059f7a8 break
0059f430 memset(&var_110_0x80_size, 0, 0x80)
0059f460 void var_90
0059f460 memset(&var_90, 0, 0x80)
0059f4a0 sprintf(&var_90, 0x79ca14, 0x79ca1c, ctr + 1, var_138, var_134, var_130, var_12c, var_128) {"%s%d"} {"domain"}
0059f648 if (zx_file_readcfg(file: "/mnt/zx_udp_push_config.ini", char *section: 0x79c980, headername: &var_90, output: &var_110_0x80_size) != 0) {"[NET]"}
0059f648 $v0_1 = 0xffffffff
0059f64c break
0059f524 memset((ctr << 7) + 0x88287c, 0, 0x80)
0059f554 if (strlen(&var_110_0x80_size) u< 0x80)
0059f5b4 strncpy((ctr << 7) + 0x88287c, &var_110_0x80_size, strlen(&var_110_0x80_size) - 1) //[3]
0059f5dc var_138 = 0xb2
0059f5e4 var_134 = 0x28
0059f5f0 var_130 = 0x79ca24 {"%s:%s"}
0059f5f8 var_12c = &var_90
0059f5fc var_128 = (ctr << 7) + 0x88287c
0059f624 dzlog(0x79c99c, 0x17, 0x79dd8c, 0x19, 0xb2, 0x28, 0x79ca24, var_12c, var_128) {"src/zx_push_interface.c"} {"%s:%s"} {"read_udp_push_config_file"}
0059f63c ctr = ctr + 1
At [1], we see the domain_total field being pulled out of the config file. This value serves as an upper-bound loop condition for the loop at [2]. As our ctr variable increments until it reaches s_udp_server_total_nums, the domain%d fields are again searched for. If a match is found, then we again write to ((ctr << 7) + 0x88287c, an arbitrary value since we control the contents of the file. Thus, for example, with a domain100000=aaaaaaaaaaaaaa... inside of the config file, an out-of-bounds write occurs, resulting in code execution.
Timeline
2021-09-30 - Vendor Disclosure
2021-11-22 - Vendor Patched
2021-11-29 - Public Release
Discovered by Lilith >_> of Cisco Talos.