CodeQL documentation

Authentication bypass by spoofing

ID: cpp/user-controlled-bypass
Kind: path-problem
Security severity: 8.1
Severity: warning
Precision: medium
   - security
   - external/cwe/cwe-290
Query suites:
   - cpp-security-extended.qls
   - cpp-security-and-quality.qls

Click to see the query in the CodeQL repository

Code which relies on an IP address or domain name for authentication can be exploited by an attacker who spoofs their address.


IP address verification can be a useful part of an authentication scheme, but it should not be the single factor required for authentication. Make sure that other authentication methods are also in place.


In this example (taken from CWE-290: Authentication Bypass by Spoofing), the client is authenticated by checking that its IP address is An attacker might be able to bypass this authentication by spoofing their IP address.

#define BUFFER_SIZE (4 * 1024)

void receiveData()
  int sock;
  sockaddr_in addr, addr_from;
  char buffer[BUFFER_SIZE];
  int msg_size;
  socklen_t addr_from_len;

  // configure addr
  memset(&addr, 0, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(1234);
  addr.sin_addr.s_addr = INADDR_ANY;

  // create and bind the socket
  sock = socket(AF_INET, SOCK_DGRAM, 0);
  bind(sock, (sockaddr *)&addr, sizeof(addr));

  // receive message
  addr_from_len = sizeof(addr_from);
  msg_size = recvfrom(sock, buffer, BUFFER_SIZE, 0, (sockaddr *)&addr_from, &addr_from_len);

  // BAD: the address is controllable by the user, so it
  // could be spoofed to bypass the security check below.
  if ((msg_size > 0) && (strcmp("", inet_ntoa(addr_from.sin_addr)) == 0))
    // ...


  • Common Weakness Enumeration: CWE-290.

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