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CWE-292: Trusting Self-reported DNS Name
 DescriptionDescription Summary The use of self-reported DNS names as authentication is flawed and can easily be spoofed by malicious users.
Time of Introduction
Applicable PlatformsLanguages All Common Consequences
Likelihood of ExploitHigh Demonstrative ExamplesExample 1 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. (Bad Code) Example
Language: 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;
} (Bad Code) Example
Language: Java String ip = request.getRemoteAddr(); InetAddress addr = InetAddress.getByName(ip); if (addr.getCanonicalHostName().endsWith("trustme.com")) { trusted = true;
} (Bad Code) Example
Language: 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. Example 2 In these examples, a connection is established if a request is made by a trusted host. (Bad Code) Example Languages: C and 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);
h=gethostbyname(inet_ntoa(cliAddr.sin_addr));
if (h->h_name==...) n = recvfrom(sd, msg, MAX_MSG, 0,
(struct sockaddr *) & cli, &clilen);
} (Bad Code) Example
Language: Java while(true) { DatagramPacket rp=new
DatagramPacket(rData,rData.length);
outSock.receive(rp);
String in = new String(p.getData(),0, rp.getLength());
InetAddress IPAddress = rp.getAddress();
int port = rp.getPort();
if ((rp.getHostName()==...) & (in==...)) {
out = secret.getBytes();
DatagramPacket sp =new DatagramPacket(out,out.length,
IPAddress, port);
outSock.send(sp);
}
} These examples check if a request is from a trusted host before responding to a request, but the code only verifies the hostname as stored in the request packet. An attacker can spoof the hostname, thus impersonating a trusted client. Observed Examples
Potential Mitigations
Other Notes
Relationships
Taxonomy Mappings
Related Attack Patterns
Content History
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Page Last Updated:
February 20, 2013
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