Trusting self-reported DNS name

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Overview

The use of self-reported DNS names as authentication is flawed and can easily be spoofed by malicious users.

Consequences

Authentication: Malicious users can fake authentication information by providing false DNS information.

Exposure period

  • Design: Authentication methods are generally chosen during the design phase of development.

Platform

  • Languages: All
  • Operating platforms: All

Required resources

Any

Severity

High

Likelihood of exploit

High

Avoidance and mitigation

  • Design: Use other means of identity verification that cannot be simply spoofed.

Discussion

As DNS names can be easily spoofed or mis-reported, they do not constitute a valid authentication mechanism. Alternate methods should be used if the significant authentication is necessary.

In addition, DNS name resolution as authentication would - even if it was a valid means of authentication - imply a trust relationship with the DNS servers used, as well as all of the servers they refer to.

Examples

In 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);
  h=gethostbyname(inet_ntoa(cliAddr.sin_addr));
  if (h->h_name==...)
  n = recvfrom(sd, msg, MAX_MSG, 0,
              (struct sockaddr *) & cli, &clilen);
}

In 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);
  }  
}

Related problems

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