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.
Real-world impact
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.
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Integer truncation of length value leads to heap-based buffer overflow.
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Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated.
How attackers exploit it
Step-by-step attacker path
- 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.
Vulnerable code example
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); Secure code example
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.
Prevention checklist
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.
Detection signals
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 auto-detects CWE-197 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.
Frequently asked questions What is CWE-197?
How serious is CWE-197?
What languages or platforms are affected by CWE-197?
How can I prevent CWE-197?
How does Plexicus detect and fix CWE-197?
Where can I learn more about CWE-197?
Frequently asked questions
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.
How serious is CWE-197?
MITRE rates the likelihood of exploit as Low — exploitation is uncommon, but the weakness should still be fixed when discovered.
What languages or platforms are affected by CWE-197?
MITRE lists the following affected platforms: C, C++, Java, C#.
How can I prevent CWE-197?
Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
How does Plexicus detect and fix CWE-197?
Plexicus's SAST engine matches the data-flow signature for CWE-197 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-197?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/197.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
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…
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