The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.

This can happen in signed and unsigned cases.

Integer underflow

"Integer underflow" is sometimes used to identify signedness errors in which an originally positive number becomes negative as a result of subtraction. However, there are cases of bad subtraction in which unsigned integers are involved, so it's not always a signedness issue. "Integer underflow" is occasionally used to describe array index errors in which the index is negative.

This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Impact	Details
DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Instability	Scope: Availability This weakness will generally lead to undefined behavior and therefore crashes. In the case of overflows involving loop index variables, the likelihood of infinite loops is also high.
Modify Memory	Scope: Integrity If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the wrap around results in other conditions such as buffer overflows, further memory corruption may occur.
Execute Unauthorized Code or Commands; Bypass Protection Mechanism	Scope: Confidentiality, Availability, Access Control This weakness can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.

This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Implementation

This listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

C (Undetermined Prevalence) C++ (Undetermined Prevalence) Java (Undetermined Prevalence) C# (Undetermined Prevalence)

Example 1

The following example subtracts from a 32 bit signed integer.

The example has an integer underflow. The value of i is already at the lowest negative value possible, so after subtracting 1, the new value of i is 2147483647.

Example 2

This code performs a stack allocation based on a length calculation.

Since a and b are declared as signed ints, the "a - b" subtraction gives a negative result (-1). However, since len is declared to be unsigned, len is cast to an extremely large positive number (on 32-bit systems - 4294967295). As a result, the buffer buf[len] declaration uses an extremely large size to allocate on the stack, very likely more than the entire computer's memory space.

Miscalculations usually will not be so obvious. The calculation will either be complicated or the result of an attacker's input to attain the negative value.

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Ordinality	Description
Primary	(where the weakness exists independent of other weaknesses)
Resultant	(where the weakness is typically related to the presence of some other weaknesses)