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CWE

Incorrect Calculation

ID: 682		Date: (C)2012-05-14 (M)2022-10-10
Type: weakness		Status: DRAFT
Abstraction Type: Class

Description

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

Extended Description

When software 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.

Likelihood of Exploit: High

Applicable Platforms
Language Class: All

Time Of Introduction

Architecture and Design
Implementation

Related Attack Patterns

Common Consequences

Scope	Technical Impact	Notes
Availability	DoS: crash / exit / restart	If the incorrect calculation causes the program to move into an unexpected state, it may lead to a crash or impairment of service.
Integrity Confidentiality Availability	DoS: crash / exit / restart DoS: resource consumption (other) Execute unauthorized code or commands	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).
Access_Control	Gain privileges / assume identity	In the context of privilege or permissions assignment, an incorrect calculation can provide an attacker with access to sensitive resources.
Access_Control	Bypass protection mechanism	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.

Detection Methods

Name	Description	Effectiveness	Notes
Manual Analysis	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.	High

Potential Mitigations

Phase	Strategy	Description
Implementation		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	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		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 Libraries or Frameworks	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	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.
Testing		Use automated static analysis tools that target this type of weakness. Many modern techniques use data flow analysis to minimize the number of false positives. This is not a perfect solution, since 100% accuracy and coverage are not feasible.
Testing		Use dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Relationships

Related CWE	Type	View	Chain
CWE-682 ChildOf CWE-907	Category	CWE-888

Demonstrative Examples (Details)

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name
CERT C Secure Coding	FLP32-C	Prevent or detect domain and range errors in math functions
CERT C Secure Coding	FLP33-C	Convert integers to floating point for floating point operations
CERT C Secure Coding	INT07-C	Use only explicitly signed or unsigned char type for numeric values
CERT C Secure Coding	INT13-C	Use bitwise operators only on unsigned operands
CERT C++ Secure Coding	INT07-CPP	Use only explicitly signed or unsigned char type for numeric values
CERT C++ Secure Coding	INT10-CPP	Do not assume a positive remainder when using the % operator
CERT C++ Secure Coding	INT13-CPP	Use bitwise operators only on unsigned operands
CERT C++ Secure Coding	FLP32-CPP	Prevent or detect domain and range errors in math functions
CERT C++ Secure Coding	FLP33-CPP	Convert integers to floating point for floating point operations

References:

David LeBlanc Niels Dekker .SafeInt.
Michael Howard David LeBlanc John Viega .24 Deadly Sins of Software Security. McGraw-Hill. Section:'"Sin 7: Integer Overflows." Page 119'. Published on 2010.
Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 6, "Signed Integer Boundaries", Page 220.'. Published on 2006.


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