Description
Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.
When a primitive is cast to a smaller primitive, the high order bits of the large value are lost in the conversion, potentially resulting in an unexpected value that is not equal to the original value. This value may be required as an index into a buffer, a loop iterator, or simply necessary state data. In any case, the value cannot be trusted and the system will be in an undefined state. While this method may be employed viably to isolate the low bits of a value, this usage is rare, and truncation usually implies that an implementation error has occurred.
Potential Impact
Integrity
Modify Memory
Demonstrative Examples
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);Int MAXINT: 2147483647Short MAXINT: -1...
// 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);
// 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);
}......
// 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
...}
}...Mitigations & Prevention
Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
Detection Methods
- Fuzzing High — 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,
- 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 sea
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2020-17087 | 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. |
| CVE-2009-0231 | Integer truncation of length value leads to heap-based buffer overflow. |
| CVE-2008-3282 | Size of a particular type changes for 64-bit platforms, leading to an integer truncation in document processor causes incorrect index to be generated. |
Related Weaknesses
Taxonomy Mappings
- PLOVER: — Numeric truncation error
- CLASP: — Truncation error
- CERT C Secure Coding: FIO34-C — Distinguish between characters read from a file and EOF or WEOF
- CERT C Secure Coding: FLP34-C — Ensure that floating point conversions are within range of the new type
- CERT C Secure Coding: INT02-C — Understand integer conversion rules
- CERT C Secure Coding: INT05-C — Do not use input functions to convert character data if they cannot handle all possible inputs
- CERT C Secure Coding: INT31-C — Ensure that integer conversions do not result in lost or misinterpreted data
- The CERT Oracle Secure Coding Standard for Java (2011): NUM12-J — Ensure conversions of numeric types to narrower types do not result in lost or misinterpreted data
- Software Fault Patterns: SFP1 — Glitch in computation
Frequently Asked Questions
What is CWE-197?
CWE-197 (Numeric Truncation Error) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.
How can CWE-197 be exploited?
Attackers can exploit CWE-197 (Numeric Truncation Error) to modify memory. This weakness is typically introduced during the Implementation phase of software development.
How do I prevent CWE-197?
Key mitigations include: Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
What is the severity of CWE-197?
CWE-197 is classified as a Base-level weakness (Medium abstraction). It has been observed in 3 real-world CVEs.