Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.
CWE-469 Base Draft
Use of Pointer Subtraction to Determine Size
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and…
Definition
What is CWE-469?
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and potentially dangerous result.
Pointer subtraction is a valid C/C++ operation, but it only yields a meaningful size or element count when both pointers point within the same contiguous memory allocation (like a single array or buffer). When developers use this trick on pointers from different allocations, the calculation produces a nonsensical value based on the arbitrary memory distance between the two chunks. This flawed size is then often used in buffer operations, leading to out-of-bounds reads or writes, memory corruption, and crashes.
Detecting these flaws manually is tricky because the code looks mathematically simple. While SAST tools can flag the pattern, Plexicus uses AI to analyze the pointer origins and suggest the correct fix—such as storing the allocation size separately—saving hours of debugging. Managing this at scale across a large codebase is difficult; an ASPM like Plexicus can help you track and remediate these subtle memory flaws across your entire application stack.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-469
Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.
- 2
Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.
- 3
Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.
- 4
Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.
Verwundbares Codebeispiel
Vulnerable C
The following example contains the method size that is used to determine the number of nodes in a linked list. The method is passed a pointer to the head of the linked list.
struct node {
int data;
struct node* next;
};
```
// Returns the number of nodes in a linked list from*
*// the given pointer to the head of the list.*
int size(struct node* head) {
```
struct node* current = head;
struct node* tail;
while (current != NULL) {
tail = current;
current = current->next;
}
return tail - head;
}
```
// other methods for manipulating the list*
... Sicheres Codebeispiel
Secure C
However, the method creates a pointer that points to the end of the list and uses pointer subtraction to determine the number of nodes in the list by subtracting the tail pointer from the head pointer. There no guarantee that the pointers exist in the same memory area, therefore using pointer subtraction in this way could return incorrect results and allow other unintended behavior. In this example a counter should be used to determine the number of nodes in the list, as shown in the following code.
...
int size(struct node* head) {
struct node* current = head;
int count = 0;
while (current != NULL) {
count++;
current = current->next;
}
return count;
} 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-469
- Implementation Save an index variable. This is the recommended solution. Rather than subtract pointers from one another, use an index variable of the same size as the pointers in question. Use this variable to "walk" from one pointer to the other and calculate the difference. Always validate this number.
Erkennungssignale
How to detect CWE-469
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 erkennt CWE-469 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.
Häufig gestellte Fragen Was ist CWE-469?
Wie gravierend ist CWE-469?
Welche Sprachen oder Plattformen sind von CWE-469 betroffen?
Wie kann ich CWE-469 verhindern?
Wie erkennt und behebt Plexicus CWE-469?
Wo erfahre ich mehr über CWE-469?
Frequently asked questions
Was ist CWE-469?
This vulnerability occurs when a program calculates a size or offset by subtracting two memory pointers, but the pointers point to locations in different memory blocks, leading to an incorrect and potentially dangerous result.
Wie gravierend ist CWE-469?
MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.
Welche Sprachen oder Plattformen sind von CWE-469 betroffen?
MITRE lists the following affected platforms: C, C++.
Wie kann ich CWE-469 verhindern?
Save an index variable. This is the recommended solution. Rather than subtract pointers from one another, use an index variable of the same size as the pointers in question. Use this variable to "walk" from one pointer to the other and calculate the difference. Always validate this number.
Wie erkennt und behebt Plexicus CWE-469?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-469 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-469?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/469.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-469
CWE-682 Parent
Incorrect Calculation
This vulnerability occurs when software performs a calculation that produces wrong or unexpected results, which are then used to make…
CWE-128 Sibling
Wrap-around Error
A wrap-around error happens when a variable exceeds the maximum value its data type can hold, causing it to unexpectedly reset to a very…
CWE-131 Sibling
Incorrect Calculation of Buffer Size
This vulnerability occurs when a program miscalculates the amount of memory needed for a buffer, potentially leading to a buffer overflow…
CWE-1335 Sibling
Incorrect Bitwise Shift of Integer
This vulnerability occurs when a program attempts to shift an integer's bits by an invalid amount—either a negative number or a value…
CWE-1339 Sibling
Insufficient Precision or Accuracy of a Real Number
This vulnerability occurs when a program uses a data type or algorithm that cannot accurately represent or calculate the fractional part…
CWE-135 Sibling
Incorrect Calculation of Multi-Byte String Length
This vulnerability occurs when software incorrectly measures the length of strings containing multi-byte or wide characters, leading to…
CWE-190 Sibling
Integer Overflow or Wraparound
Integer overflow or wraparound occurs when a calculation produces a numeric result that exceeds the maximum value a variable can hold.…
CWE-191 Sibling
Integer Underflow (Wrap or Wraparound)
Integer underflow occurs when a subtraction operation results in a value smaller than the data type's minimum limit, causing the value to…
CWE-193 Sibling
Off-by-one Error
An off-by-one error occurs when a program incorrectly calculates a boundary, such as a loop counter or array index, by being one unit too…
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