CWE-686 Variant Draft

Function Call With Incorrect Argument Type

This vulnerability occurs when a program calls a function or method but passes an argument of the wrong data type, which can cause unexpected behavior or security flaws.

Definition

What is CWE-686?

This vulnerability occurs when a program calls a function or method but passes an argument of the wrong data type, which can cause unexpected behavior or security flaws.
This issue is most common in loosely typed languages like JavaScript or PHP, where the language doesn't enforce strict type checks at runtime. It can also happen in strongly typed languages when using features like variable argument lists or implicit type conversions, where the compiler cannot catch the mismatch before the code runs. When a function receives a type it doesn't expect—like a string instead of a number—it may crash, produce incorrect results, or trigger other weaknesses like buffer overflows or injection flaws. Developers should use explicit type checking, validation, and modern language features (like TypeScript or strict mode) to prevent these errors.
Real-world impact

Real-world CVEs caused by CWE-686

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-686

  • Testing Because this function call often produces incorrect behavior it will usually be detected during testing or normal operation of the product. During testing exercise all possible control paths will typically expose this weakness except in rare cases when the incorrect function call accidentally produces the correct results or if the provided argument type is very similar to the expected argument type.
Detection signals

How to detect CWE-686

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.

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Frequently asked questions

Frequently asked questions

What is CWE-686?

This vulnerability occurs when a program calls a function or method but passes an argument of the wrong data type, which can cause unexpected behavior or security flaws.

How serious is CWE-686?

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-686?

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

How can I prevent CWE-686?

Because this function call often produces incorrect behavior it will usually be detected during testing or normal operation of the product. During testing exercise all possible control paths will typically expose this weakness except in rare cases when the incorrect function call accidentally produces the correct results or if the provided argument type is very similar to the expected argument type.

How does Plexicus detect and fix CWE-686?

Plexicus's SAST engine matches the data-flow signature for CWE-686 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-686?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/686.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-686

CWE-628 Parent

Function Call with Incorrectly Specified Arguments

This weakness occurs when a function is called with arguments that are incorrectly specified, causing the function to behave in an…

CWE-683 Sibling

Function Call With Incorrect Order of Arguments

This vulnerability occurs when a program calls a function but supplies the arguments in the wrong order, which can cause unexpected…

CWE-685 Sibling

Function Call With Incorrect Number of Arguments

This weakness occurs when a program calls a function, method, or subroutine but provides the wrong number of arguments—either too many or…

CWE-687 Sibling

Function Call With Incorrectly Specified Argument Value

This vulnerability occurs when a function is called with an argument that holds an incorrect or unexpected value, leading to unintended…

CWE-688 Sibling

Function Call With Incorrect Variable or Reference as Argument

This vulnerability occurs when a function is called with the wrong variable or reference passed as an argument. This simple coding mistake…

Resources

Further reading

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