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

Resultant

Implementation

Architecture and Design

Access Control
Bypass Protection Mechanism
Gain Privileges or Assume Identity
This weakness can allow an attacker to access resources which are not otherwise accessible without proper authentication.

The following code authenticates users.

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.

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);}}

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.

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;}

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

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-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.
https://www.cve.org/CVERecord?id=CVE-2022-30319

CVE-2009-1048
VOIP product allows authentication bypass using 127.0.0.1 in the Host header.
https://www.cve.org/CVERecord?id=CVE-2009-1048

Authentication bypass by spoofing

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

This can be resultant from insufficient verification.

PLOVER
2006-07-19
Draft 3
2006-07-19

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

CWE Content Team
MITRE
2013-07-17
updated Relationships

CWE Content Team
MITRE
2014-02-18
updated Related_Attack_Patterns

CWE Content Team
MITRE
2014-07-30
updated Demonstrative_Examples, Relationships

CWE Content Team
MITRE
2017-05-03
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples, Modes_of_Introduction, Relationships

CWE Content Team
MITRE
2019-06-20
updated Related_Attack_Patterns, Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2021-07-20
updated Related_Attack_Patterns

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated Relationships

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Modes_of_Introduction, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2023-10-26
updated Observed_Examples

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Relationships, Time_of_Introduction, Weakness_Ordinalities