CWE-563 Base Draft

Assignment to Variable without Use

This vulnerability occurs when a value is stored in a variable, but that variable is never read or used in subsequent code, creating a 'dead store.'

Definition

What is CWE-563?

This vulnerability occurs when a value is stored in a variable, but that variable is never read or used in subsequent code, creating a 'dead store.'
A dead store happens when a variable is assigned a value, only to be immediately overwritten by another assignment or to fall out of scope without being referenced. This often indicates leftover code from a previous implementation or refactoring, but it can also be a subtle sign of a logic error—perhaps a critical calculation was meant to be used but was accidentally omitted. While these issues can seem minor, they clutter code, harm performance, and may mask deeper bugs. Managing this at scale is difficult; an ASPM like Plexicus can help you track and remediate these flaws across your entire stack by identifying dead stores and using AI to suggest precise clean-up actions, turning security hygiene into an automated process.
Real-world impact

Real-world CVEs caused by CWE-563

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 C

The following code excerpt assigns to the variable r and then overwrites the value without using it.

Vulnerable C 
r = getName();
  r = getNewBuffer(buf);
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-563

  • Implementation Remove unused variables from the code.
Detection signals

How to detect CWE-563

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.)

Plexicus auto-fix

Plexicus auto-detects CWE-563 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-563?

This vulnerability occurs when a value is stored in a variable, but that variable is never read or used in subsequent code, creating a 'dead store.'

How serious is CWE-563?

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-563?

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

How can I prevent CWE-563?

Remove unused variables from the code.

How does Plexicus detect and fix CWE-563?

Plexicus's SAST engine matches the data-flow signature for CWE-563 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-563?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/563.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-563

CWE-1164 Parent

Irrelevant Code

Irrelevant code refers to sections of a program that have no impact on its execution, data, or logic. Removing this code would not change…

CWE-107 Sibling

Struts: Unused Validation Form

This vulnerability occurs when a Struts application contains validation form definitions that are no longer linked to any active form or…

CWE-1071 Sibling

Empty Code Block

An empty code block occurs when a section of source code, such as a conditional statement or function body, contains no executable…

CWE-110 Sibling

Struts: Validator Without Form Field

This vulnerability occurs when a Struts application's validation configuration file references form fields that no longer exist in the…

CWE-561 Sibling

Dead Code

Dead code refers to sections of a program that can never run during normal execution, effectively making them inactive and unreachable.

Resources

Further reading

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