CWE-291 Variant Incomplete High likelihood

Reliance on IP Address for Authentication

This vulnerability occurs when a system uses a client's IP address as the sole or primary method to verify their identity.

Definition

What is CWE-291?

This vulnerability occurs when a system uses a client's IP address as the sole or primary method to verify their identity.
Relying solely on an IP address for authentication is a significant security risk because these addresses are not reliable proof of identity. Attackers can easily forge, or 'spoof,' the source IP address in the network packets they send. While this manipulation makes response packets return to the faked address, a determined attacker can intercept this return traffic, especially if they are on the same network segment as the target system. Therefore, an IP address should only ever be used as one component within a broader, multi-factor authentication strategy. It can provide a useful layer of context, such as for geolocation or anomaly detection, but it must be combined with stronger credentials like API keys, tokens, or certificates. Using it alone is equivalent to trusting a return address on an envelope as definitive proof of the sender's identity.
Real-world impact

Real-world CVEs caused by CWE-291

  • 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.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable C

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

Vulnerable 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);
  	if (inet_ntoa(cli.sin_addr)==getTrustedAddress()) {
  		n = recvfrom(sd, msg, MAX_MSG, 0, (struct sockaddr *) & cli, &clilen);
  	}
  }
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-291

  • Architecture and Design Use other means of identity verification that cannot be simply spoofed. Possibilities include a username/password or certificate.
Detection signals

How to detect CWE-291

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-291 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-291?

This vulnerability occurs when a system uses a client's IP address as the sole or primary method to verify their identity.

How serious is CWE-291?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-291?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-291?

Use other means of identity verification that cannot be simply spoofed. Possibilities include a username/password or certificate.

How does Plexicus detect and fix CWE-291?

Plexicus's SAST engine matches the data-flow signature for CWE-291 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-291?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/291.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-291

CWE-290 Parent

Authentication Bypass by Spoofing

This weakness occurs when an application's authentication system can be tricked into accepting forged or manipulated credentials, allowing…

CWE-293 Sibling

Using Referer Field for Authentication

This vulnerability occurs when a web application uses the HTTP Referer header as a sole or primary method for authentication or…

CWE-350 Sibling

Reliance on Reverse DNS Resolution for a Security-Critical Action

This vulnerability occurs when an application uses a reverse DNS lookup on an IP address to get a hostname and then uses that hostname for…

Resources

Further reading

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