CWE-687 Variant Draft

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 program behavior or security flaws.

Definition

What is CWE-687?

This vulnerability occurs when a function is called with an argument that holds an incorrect or unexpected value, leading to unintended program behavior or security flaws.
Incorrect argument values often happen due to simple mistakes like mixing up parameter order, using hard-coded magic numbers, or passing a variable that hasn't been properly validated. For example, calling a file permission function with a value meant for a buffer size can expose sensitive data or crash the application. These errors are subtle because the code compiles and runs, but the logic is fundamentally broken, creating a gap between what the developer intended and what actually executes. Finding these mismatches manually in a large codebase is like searching for a needle in a haystack. While SAST tools can flag suspicious patterns, Plexicus uses AI to not only detect these flaws but also generate the precise code fix, transforming a generic warning into an actionable correction. This saves significant manual review time and helps ensure that the function receives the exact value it was designed to handle, closing the door on a wide range of downstream vulnerabilities.
Real-world impact

Real-world CVEs caused by CWE-687

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 Perl

This Perl code intends to record whether a user authenticated successfully or not, and to exit if the user fails to authenticate. However, when it calls ReportAuth(), the third argument is specified as 0 instead of 1, so it does not exit.

Vulnerable Perl 
sub ReportAuth {
  	my ($username, $result, $fatal) = @_;
  	PrintLog("auth: username=%s, result=%d", $username, $result);
  	if (($result ne "success") && $fatal) {
  		die "Failed!\n";
  	}
  }
  sub PrivilegedFunc
  {
  	my $result = CheckAuth($username);
  	ReportAuth($username, $result, 0);
  	DoReallyImportantStuff();
  }
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-687

  • 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-687

Manual Static Analysis

This might require an understanding of intended program behavior or design to determine whether the value is incorrect.

Plexicus auto-fix

Plexicus auto-detects CWE-687 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-687?

This vulnerability occurs when a function is called with an argument that holds an incorrect or unexpected value, leading to unintended program behavior or security flaws.

How serious is CWE-687?

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-687?

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

How can I prevent CWE-687?

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-687?

Plexicus's SAST engine matches the data-flow signature for CWE-687 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-687?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/687.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-687

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-686 Sibling

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…

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…

CWE-560 Child

Use of umask() with chmod-style Argument

This vulnerability occurs when a program incorrectly uses the `umask()` system call with an argument formatted for `chmod()`, leading to…

Resources

Further reading

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