CWE-843 Base Incomplete

Access of Resource Using Incompatible Type ('Type Confusion')

Type confusion occurs when a program creates a resource—like a pointer, object, or variable—with one data type, but later incorrectly accesses it as a different, incompatible type.

Definition

What is CWE-843?

Type confusion occurs when a program creates a resource—like a pointer, object, or variable—with one data type, but later incorrectly accesses it as a different, incompatible type.
This mismatch can cause the program to misinterpret the data in memory, leading to logical errors, crashes, or unexpected behavior because the resource lacks the properties the code expects. In memory-unsafe languages like C and C++, this often results in dangerous out-of-bounds memory access, corrupting data or creating security vulnerabilities. While commonly seen with C/C++ unions when parsing complex data structures, type confusion can appear in many languages. For instance, PHP might fail if an array is passed where a single value is required, and languages like Perl that perform automatic type conversion can also introduce subtle bugs when variables are accessed as unintended types.
Auswirkungen in der Praxis

Real-world CVEs caused by CWE-843

  • CVE-2010-4577

    Type confusion in CSS sequence leads to out-of-bounds read.

  • CVE-2011-0611

    Size inconsistency allows code execution, first discovered when it was actively exploited in-the-wild.

  • CVE-2010-0258

    Improperly-parsed file containing records of different types leads to code execution when a memory location is interpreted as a different object than intended.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

  1. 1

    The following code uses a union to support the representation of different types of messages. It formats messages differently, depending on their type.

  2. 2

    The code intends to process the message as a NAME_TYPE, and sets the default message to "Hello World." However, since both buf.name and buf.nameID are part of the same union, they can act as aliases for the same memory location, depending on memory layout after compilation.

  3. 3

    As a result, modification of buf.nameID - an int - can effectively modify the pointer that is stored in buf.name - a string.

  4. 4

    Execution of the program might generate output such as:

  5. 5

    ``` Pointer of name is 10830 Pointer of name is now 10831 Message: ello World ```

Verwundbares Codebeispiel

Vulnerable C

The following code uses a union to support the representation of different types of messages. It formats messages differently, depending on their type.

Verwundbar C 
#define NAME_TYPE 1
  #define ID_TYPE 2
  struct MessageBuffer
  {
  	int msgType;
  	union {
  		char *name;
  		int nameID;
  	};
  };
  int main (int argc, char **argv) {
  		struct MessageBuffer buf;
  		char *defaultMessage = "Hello World";
  		buf.msgType = NAME_TYPE;
  		buf.name = defaultMessage;
  		printf("Pointer of buf.name is %p\n", buf.name);
```
/* This particular value for nameID is used to make the code architecture-independent. If coming from untrusted input, it could be any value. */* 
  		
  		buf.nameID = (int)(defaultMessage + 1);
  		printf("Pointer of buf.name is now %p\n", buf.name);
  		if (buf.msgType == NAME_TYPE) {
  		```
  			printf("Message: %s\n", buf.name);
  		}
  		else {
  			printf("Message: Use ID %d\n", buf.nameID);
  		}
  }
Sicheres Codebeispiel

Secure pseudo

Sicher 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.
Präventions-Checkliste

How to prevent CWE-843

  • 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.
Erkennungssignale

How to detect CWE-843

SAST High

Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.

DAST Moderate

Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.

Runtime Moderate

Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.

Code review Moderate

Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.

Plexicus Auto-Fix

Plexicus erkennt CWE-843 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

Demo anfordern Plexicus kostenlos testen
Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-843?

Type confusion occurs when a program creates a resource—like a pointer, object, or variable—with one data type, but later incorrectly accesses it as a different, incompatible type.

Wie gravierend ist CWE-843?

MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.

Welche Sprachen oder Plattformen sind von CWE-843 betroffen?

MITRE lists the following affected platforms: C, C++.

Wie kann ich CWE-843 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-843?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-843 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-843?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/843.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-843

CWE-704 Parent

Incorrect Type Conversion or Cast

This vulnerability occurs when software incorrectly changes data from one type to another, leading to unexpected behavior or security flaws.

CWE-1389 Sibling

Incorrect Parsing of Numbers with Different Radices

This vulnerability occurs when software processes numeric input expecting standard decimal numbers (base 10), but fails to handle inputs…

CWE-588 Sibling

Attempt to Access Child of a Non-structure Pointer

This vulnerability occurs when code incorrectly treats a pointer to a basic data type (like an integer) as if it points to a structured…

CWE-681 Sibling

Incorrect Conversion between Numeric Types

This vulnerability occurs when a program converts a value from one numeric type to another (like a 64-bit integer to a 32-bit integer) and…

CWE-119 Kann vorausgehen

Improper Restriction of Operations within the Bounds of a Memory Buffer

This vulnerability occurs when software accesses a memory buffer but reads from or writes to a location outside its allocated boundary.…

Ressourcen

Further reading

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