CWE-290: Authentication Bypass by Spoofing

Description

This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.

Potential Impact

Access Control

Bypass Protection Mechanism, Gain Privileges or Assume Identity

Demonstrative Examples

The following code authenticates users.

Bad

String sourceIP = request.getRemoteAddr();if (sourceIP != null && sourceIP.equals(APPROVED_IP)) {authenticated = true;}

The authentication mechanism implemented relies on an IP address for source validation. If an attacker is able to spoof the IP, they may be able to bypass the authentication mechanism.

Both of these examples check if a request is from a trusted address before responding to the request.

Bad

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);}}

Bad

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.

Bad

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

String ip = request.getRemoteAddr();InetAddress addr = InetAddress.getByName(ip);if (addr.getCanonicalHostName().endsWith("trustme.com")) {trusted = true;}

Bad

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.

Real-World CVE Examples

CVE ID	Description
CVE-2022-30319	S-bus functionality in a home automation product performs access control using an IP allowlist, which can be bypassed by a forged IP address.
CVE-2009-1048	VOIP product allows authentication bypass using 127.0.0.1 in the Host header.

Taxonomy Mappings

PLOVER: — Authentication bypass by spoofing

Frequently Asked Questions

What is CWE-290?

CWE-290 (Authentication Bypass by Spoofing) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.

How can CWE-290 be exploited?

Attackers can exploit CWE-290 (Authentication Bypass by Spoofing) to bypass protection mechanism, gain privileges or assume identity. This weakness is typically introduced during the Implementation, Architecture and Design phase of software development.

How do I prevent CWE-290?

Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.

What is the severity of CWE-290?

CWE-290 is classified as a Base-level weakness (Medium abstraction). It has been observed in 2 real-world CVEs.