CWE-475 Base Incomplete

Undefined Behavior for Input to API

This API function exhibits unpredictable or undefined behavior when its control parameter is not set to the exact, required value.

Definition

What is CWE-475?

This API function exhibits unpredictable or undefined behavior when its control parameter is not set to the exact, required value.
This vulnerability occurs when a function's behavior depends on a specific control parameter, like a mode selector or a flag. If a developer passes any other value, the function's actions become undefined by the API specification. This can lead to crashes, data corruption, or unexpected system states because the underlying code isn't designed to handle those inputs. To prevent this, developers must strictly adhere to the API's documented requirements for parameter values. Always validate inputs before passing them to such functions and implement robust error handling for invalid cases. Relying on observed behavior from undefined states is dangerous, as it can change across different compilers, system updates, or hardware.
Real-world impact

Real-world CVEs caused by CWE-475

No public CVE references are linked to this CWE in MITRE's catalog yet.

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 pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
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-475

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-475

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

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Frequently asked questions

Frequently asked questions

What is CWE-475?

This API function exhibits unpredictable or undefined behavior when its control parameter is not set to the exact, required value.

How serious is CWE-475?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-475?

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

How can I prevent CWE-475?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-475?

Plexicus's SAST engine matches the data-flow signature for CWE-475 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-475?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/475.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-475

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Resources

Further reading

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