COMMON WEAKNESS ENUMERATIONDraft

CWE-682

Incorrect Calculation

The product performs a calculation that generates incorrect or unintended results that are later used in security-critical decisions or resource management.

Abstraction

Pillar

Structure

Simple

Likelihood of Exploit

High

Understand the problem

What is the problem?

The product performs a calculation that generates incorrect or unintended results that are later used in security-critical decisions or resource management.

Extended description

When product performs a security-critical calculation incorrectly, it might lead to incorrect resource allocations, incorrect privilege assignments, or failed comparisons among other things. Many of the direct results of an incorrect calculation can lead to even larger problems such as failed protection mechanisms or even arbitrary code execution.

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

Risk

What does successful exploitation lead to?

DoS: Crash, Exit, or Restart

Affected security scopes: Availability

If the incorrect calculation causes the program to move into an unexpected state, it may lead to a crash or impairment of service.
DoS: Crash, Exit, or RestartDoS: Resource Consumption (Other)Execute Unauthorized Code or Commands

Affected security scopes: Integrity, Confidentiality, Availability

If the incorrect calculation is used in the context of resource allocation, it could lead to an out-of-bounds operation (CWE-119) leading to a crash or even arbitrary code execution. Alternatively, it may result in an integer overflow (CWE-190) and / or a resource consumption problem (CWE-400).
Gain Privileges or Assume Identity

Affected security scopes: Access Control

In the context of privilege or permissions assignment, an incorrect calculation can provide an attacker with access to sensitive resources.
Bypass Protection Mechanism

Affected security scopes: Access Control

If the incorrect calculation leads to an insufficient comparison (CWE-697), it may compromise a protection mechanism such as a validation routine and allow an attacker to bypass the security-critical code.

Defence

How is it prevented and fixed?

Implementation

Implementation-phase defence

Detail
Understand your programming language's underlying representation and how it interacts with numeric calculation. Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, "not-a-number" calculations, and how your language handles numbers that are too large or too small for its underlying representation.

Implementation

Input Validation

Detail
Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.

Implementation

Implementation-phase defence

Detail
Use the appropriate type for the desired action. For example, in C/C++, only use unsigned types for values that could never be negative, such as height, width, or other numbers related to quantity.

Architecture and Design

Language Selection

Detail
Use languages, libraries, or frameworks that make it easier to handle numbers without unexpected consequences. Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++).

Architecture and Design

Libraries or Frameworks

Detail
Use languages, libraries, or frameworks that make it easier to handle numbers without unexpected consequences. Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++).

Implementation

Compilation or Build Hardening

Detail
Examine compiler warnings closely and eliminate problems with potential security implications, such as signed / unsigned mismatch in memory operations, or use of uninitialized variables. Even if the weakness is rarely exploitable, a single failure may lead to the compromise of the entire system.

Verification

How is it detected?

Manual Analysis

High
This weakness can be detected using tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session. Specifically, manual static analysis is useful for evaluating the correctness of allocation calculations. This can be useful for detecting overflow conditions (CWE-190) or similar weaknesses that might have serious security impacts on the program.

These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

Automated Static Analysis

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.)

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, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.