This attack-focused weakness is caused by improperly implemented authentication schemes that are subject to spoofing attacks. 1000 699 Weakness ChildOf 592 888 Category ChildOf 902 This can be resultant from insufficient verification. Architecture and Design Implementation Access_Control Bypass protection mechanism Gain privileges / assume identity This weakness can allow an attacker to access resources which are not otherwise accessible without proper authentication. Here, an authentication mechanism implemented in Java relies on an IP address for source validation. If an attacker is able to spoof the IP, however, he may be able to bypass such an authentication mechanism. Java String sourceIP = request.getRemoteAddr(); if (sourceIP != null && sourceIP.equals(APPROVED_IP)) { authenticated = true; } Both of these examples check if a request is from a trusted address before responding to the request. C C++ sd = socket(AF_INET, SOCK_DGRAM, 0); serv.sin_family = AF_INET; serv.sin_addr.s_addr = htonl(INADDR_ANY); servr.sin_port = htons(1008); bind(sd, (struct sockaddr *) & serv, sizeof(serv)); while (1) { memset(msg, 0x0, MAX_MSG); clilen = sizeof(cli); if (inet_ntoa(cli.sin_addr)==getTrustedAddress()) { n = recvfrom(sd, msg, MAX_MSG, 0, (struct sockaddr *) & cli, &clilen); } } Java while(true) { DatagramPacket rp=new DatagramPacket(rData,rData.length); outSock.receive(rp); String in = new String(p.getData(),0, rp.getLength()); InetAddress clientIPAddress = rp.getAddress(); int port = rp.getPort(); if (isTrustedAddress(clientIPAddress) & secretKey.equals(in)) { out = secret.getBytes(); DatagramPacket sp =new DatagramPacket(out,out.length, IPAddress, port); outSock.send(sp); } } The code only verifies the address as stored in the request packet. An attacker can spoof this address, thus impersonating a trusted client The following code samples use a DNS lookup in order to decide whether or not an inbound request is from a trusted host. If an attacker can poison the DNS cache, they can gain trusted status. C struct hostent *hp;struct in_addr myaddr; char* tHost = "trustme.example.com"; myaddr.s_addr=inet_addr(ip_addr_string); hp = gethostbyaddr((char *) &myaddr, sizeof(struct in_addr), AF_INET); if (hp && !strncmp(hp->h_name, tHost, sizeof(tHost))) { trusted = true; } else { trusted = false; } Java String ip = request.getRemoteAddr(); InetAddress addr = InetAddress.getByName(ip); if (addr.getCanonicalHostName().endsWith("trustme.com")) { trusted = true; } C# IPAddress hostIPAddress = IPAddress.Parse(RemoteIpAddress); IPHostEntry hostInfo = Dns.GetHostByAddress(hostIPAddress); if (hostInfo.HostName.EndsWith("trustme.com")) { trusted = true; } IP addresses are more reliable than DNS names, but they can also be spoofed. Attackers can easily forge the source IP address of the packets they send, but response packets will return to the forged IP address. To see the response packets, the attacker has to sniff the traffic between the victim machine and the forged IP address. In order to accomplish the required sniffing, attackers typically attempt to locate themselves on the same subnet as the victim machine. Attackers may be able to circumvent this requirement by using source routing, but source routing is disabled across much of the Internet today. In summary, IP address verification can be a useful part of an authentication scheme, but it should not be the single factor required for authentication. CVE-2009-1048 VOIP product allows authentication bypass using 127.0.0.1 in the Host header. Mark Dowd John McDonald Justin Schuh The Art of Software Security Assessment Chapter 3, "Spoofing and Identification", Page 72. 1st Edition Addison Wesley 2006 Authentication bypass by spoofing 21 22 459 461 59 60 94 PLOVER Sean Eidemiller Cigital 2008-07-01 added/updated demonstrative examples Eric Dalci Cigital 2008-07-01 updated Time_of_Introduction CWE Content Team MITRE 2008-09-08 updated Description, Relationships, Relationship_Notes, Taxonomy_Mappings CWE Content Team MITRE 2009-07-27 updated Relationship_Notes CWE Content Team MITRE 2011-06-01 updated Common_Consequences CWE Content Team MITRE 2012-05-11 updated Common_Consequences, Demonstrative_Examples, Observed_Examples, References, Related_Attack_Patterns, Relationships