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-197 Base Incomplete
Numeric Truncation Error
A numeric truncation error happens when a program converts a number to a smaller data type, cutting off its higher-order bits and corrupting the original value.
Definition
What is CWE-197?
A numeric truncation error happens when a program converts a number to a smaller data type, cutting off its higher-order bits and corrupting the original value.
This vulnerability occurs because converting a larger integer (like a 32-bit `int`) to a smaller one (like a 16-bit `short`) doesn't raise an error—it silently discards the most significant bits. The resulting truncated value is often completely different from what the developer intended. This corrupted data can then cause critical failures if it's used as a buffer index, a loop counter, or a piece of application state, putting the system into an unpredictable and dangerous condition.
While bitmasking to intentionally isolate low bits is a valid technique, unintentional truncation is almost always a coding bug. These errors can be subtle and spread across large codebases. Managing this at scale is difficult; an ASPM like Plexicus can help you track and remediate these flaws across your entire stack by correlating SAST findings with runtime data and suggesting precise fixes.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-197
-
Chain: integer truncation (CWE-197) causes small buffer allocation (CWE-131) leading to out-of-bounds write (CWE-787) in kernel pool, as exploited in the wild per CISA KEV.
-
Integer truncation of length value leads to heap-based buffer overflow.
-
Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
This example, while not exploitable, shows the possible mangling of values associated with truncation errors:
- 2
The above code, when compiled and run on certain systems, returns the following output:
- 3
This problem may be exploitable when the truncated value is used as an array index, which can happen implicitly when 64-bit values are used as indexes, as they are truncated to 32 bits.
- 4
In the following Java example, the method updateSalesForProduct is part of a business application class that updates the sales information for a particular product. The method receives as arguments the product ID and the integer amount sold. The product ID is used to retrieve the total product count from an inventory object which returns the count as an integer. Before calling the method of the sales object to update the sales count the integer values are converted to The primitive type short since the method requires short type for the method arguments.
- 5
However, a numeric truncation error can occur if the integer values are higher than the maximum value allowed for the primitive type short. This can cause unexpected results or loss or corruption of data. In this case the sales database may be corrupted with incorrect data. Explicit casting from a from a larger size primitive type to a smaller size primitive type should be prevented. The following example an if statement is added to validate that the integer values less than the maximum value for the primitive type short before the explicit cast and the call to the sales method.
Verwundbares Codebeispiel
Vulnerable C
This example, while not exploitable, shows the possible mangling of values associated with truncation errors:
int intPrimitive;
short shortPrimitive;
intPrimitive = (int)(~((int)0) ^ (1 << (sizeof(int)*8-1)));
shortPrimitive = intPrimitive;
printf("Int MAXINT: %d\nShort MAXINT: %d\n", intPrimitive, shortPrimitive); Sicheres Codebeispiel
Secure Java
However, a numeric truncation error can occur if the integer values are higher than the maximum value allowed for the primitive type short. This can cause unexpected results or loss or corruption of data. In this case the sales database may be corrupted with incorrect data. Explicit casting from a from a larger size primitive type to a smaller size primitive type should be prevented. The following example an if statement is added to validate that the integer values less than the maximum value for the primitive type short before the explicit cast and the call to the sales method.
...
```
// update sales database for number of product sold with product ID*
public void updateSalesForProduct(String productID, int amountSold) {
```
```
// get the total number of products in inventory database*
int productCount = inventory.getProductCount(productID);
*// make sure that integer numbers are not greater than*
*// maximum value for type short before converting*
if ((productCount < Short.MAX_VALUE) && (amountSold < Short.MAX_VALUE)) {
```
```
// convert integer values to short, the method for the*
*// sales object requires the parameters to be of type short*
short count = (short) productCount;
short sold = (short) amountSold;
*// update sales database for product*
sales.updateSalesCount(productID, count, sold);
else {
*// throw exception or perform other processing*
```
...
}
}
... 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-197
- Implementation Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
Erkennungssignale
How to detect CWE-197
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-197 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-197?
Wie gravierend ist CWE-197?
Welche Sprachen oder Plattformen sind von CWE-197 betroffen?
Wie kann ich CWE-197 verhindern?
Wie erkennt und behebt Plexicus CWE-197?
Wo erfahre ich mehr über CWE-197?
Frequently asked questions
Was ist CWE-197?
A numeric truncation error happens when a program converts a number to a smaller data type, cutting off its higher-order bits and corrupting the original value.
Wie gravierend ist CWE-197?
MITRE stuft die Exploit-Wahrscheinlichkeit als niedrig ein — eine Ausnutzung ist selten, die Schwachstelle sollte aber dennoch behoben werden, sobald sie entdeckt wird.
Welche Sprachen oder Plattformen sind von CWE-197 betroffen?
MITRE lists the following affected platforms: C, C++, Java, C#.
Wie kann ich CWE-197 verhindern?
Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
Wie erkennt und behebt Plexicus CWE-197?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-197 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-197?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/197.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-197
CWE-681 Parent
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-192 Sibling
Integer Coercion Error
An integer coercion error occurs when a program incorrectly converts, extends, or truncates a number between different data types, leading…
CWE-194 Sibling
Unexpected Sign Extension
This vulnerability occurs when a signed number from a smaller data type is moved or cast to a larger type, causing its sign bit to be…
CWE-195 Sibling
Signed to Unsigned Conversion Error
This vulnerability occurs when a signed integer (which can hold negative values) is converted to an unsigned integer (which holds only…
CWE-196 Sibling
Unsigned to Signed Conversion Error
This vulnerability occurs when a program takes an unsigned integer and converts it directly to a signed integer. If the original unsigned…
Ressourcen
Further reading
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