Wrap-around Error

Wrap around errors occur whenever a value is incremented past the maximum value for its type and therefore "wraps around" to a very small, negative, or undefined value.


Due to how addition is performed by computers, if a primitive is incremented past the maximum value possible for its storage space, the system will not recognize this, and therefore increment each bit as if it still had extra space. Because of how negative numbers are represented in binary, primitives interpreted as signed may "wrap" to very large negative values.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following image processing code allocates a table for images.

img_t table_ptr; /*struct containing img data, 10kB each*/
int num_imgs;
num_imgs = get_num_imgs();
table_ptr = (img_t*)malloc(sizeof(img_t)*num_imgs);

This code intends to allocate a table of size num_imgs, however as num_imgs grows large, the calculation determining the size of the list will eventually overflow (CWE-190). This will result in a very small list to be allocated instead. If the subsequent code operates on the list as if it were num_imgs long, it may result in many types of out-of-bounds problems (CWE-119).

See Also

SFP Secondary Cluster: Glitch in Computation

This category identifies Software Fault Patterns (SFPs) within the Glitch in Computation cluster (SFP1).

CERT C++ Secure Coding Section 08 - Memory Management (MEM)

Weaknesses in this category are related to rules in the Memory Management (MEM) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific wea...

Numeric Errors

Weaknesses in this category are related to improper calculation or conversion of numbers.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

Weakness Base Elements

This view (slice) displays only weakness base elements.

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