CWE-228 Class Incomplete

Improper Handling of Syntactically Invalid Structure

This vulnerability occurs when software fails to properly reject or process input that doesn't follow the expected format or structure, often leading to crashes or unexpected behavior.

Definition

What is CWE-228?

This vulnerability occurs when software fails to properly reject or process input that doesn't follow the expected format or structure, often leading to crashes or unexpected behavior.
When software expects data in a specific format—like JSON, XML, protocol messages, or file structures—it must rigorously validate that incoming input matches that exact syntax. If the code assumes the input is always well-formed and doesn't implement proper error handling for malformed data, attackers can exploit this by sending deliberately invalid structures. This can trigger unhandled exceptions, cause the application to crash, or bypass security checks that rely on correct parsing. To prevent this, developers should implement strict validation at all data entry points, using well-tested parsers and libraries instead of custom logic. Always define clear error-handling routines that safely reject invalid input without exposing internal details, and design systems to fail securely—defaulting to a denied state—when encountering unexpected syntax. Regular fuzz testing with invalid inputs helps uncover these hidden parsing weaknesses before attackers do.
Real-world impact

Real-world CVEs caused by CWE-228

  • CVE-2004-0270

    Anti-virus product has assert error when line length is non-numeric.

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 Java

This Android application has registered to handle a URL when sent an intent:

Vulnerable Java 
```
...* 
  IntentFilter filter = new IntentFilter("com.example.URLHandler.openURL");
  MyReceiver receiver = new MyReceiver();
  registerReceiver(receiver, filter);
  
   *...* 
  
  public class UrlHandlerReceiver extends BroadcastReceiver {
  ```
  		@Override
  		public void onReceive(Context context, Intent intent) {
  				if("com.example.URLHandler.openURL".equals(intent.getAction())) {
  					String URL = intent.getStringExtra("URLToOpen");
  					int length = URL.length();
```
...* 
  				}}}
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-228

  • 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-228

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-228 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-228?

This vulnerability occurs when software fails to properly reject or process input that doesn't follow the expected format or structure, often leading to crashes or unexpected behavior.

How serious is CWE-228?

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-228?

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

How can I prevent CWE-228?

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-228?

Plexicus's SAST engine matches the data-flow signature for CWE-228 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-228?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/228.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-228

CWE-707 Parent

Improper Neutralization

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CWE-116 Sibling

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CWE-138 Sibling

Improper Neutralization of Special Elements

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CWE-1426 Sibling

Improper Validation of Generative AI Output

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CWE-170 Sibling

Improper Null Termination

This weakness occurs when software fails to properly end a string or array with the required null character or equivalent terminator.

CWE-172 Sibling

Encoding Error

This vulnerability occurs when software incorrectly transforms data between different formats, leading to corrupted or misinterpreted…

CWE-182 Sibling

Collapse of Data into Unsafe Value

This vulnerability occurs when an application's data filtering or transformation process incorrectly merges or simplifies information,…

CWE-20 Sibling

Improper Input Validation

This vulnerability occurs when an application accepts data from an external source but fails to properly verify that the data is safe and…

CWE-240 Sibling

Improper Handling of Inconsistent Structural Elements

This vulnerability occurs when a system fails to properly manage situations where related data structures or elements should match but are…

Resources

Further reading

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