COMMON WEAKNESS ENUMERATIONIncomplete

CWE-839

Numeric Range Comparison Without Minimum Check

The product checks a value to ensure that it is less than or equal to a maximum, but it does not also verify that the value is greater than or equal to the minimum.

Soyutlama

Base

Yapı

Simple

Sömürü İhtimali

Medium

Problemi anla

Problem nedir?

The product checks a value to ensure that it is less than or equal to a maximum, but it does not also verify that the value is greater than or equal to the minimum.

Genişletilmiş açıklama

Some products use signed integers or floats even when their values are only expected to be positive or 0. An input validation check might assume that the value is positive, and only check for the maximum value. If the value is negative, but the code assumes that the value is positive, this can produce an error. The error may have security consequences if the negative value is used for memory allocation, array access, buffer access, etc. Ultimately, the error could lead to a buffer overflow or other type of memory corruption. The use of a negative number in a positive-only context could have security implications for other types of resources. For example, a shopping cart might check that the user is not requesting more than 10 items, but a request for -3 items could cause the application to calculate a negative price and credit the attacker's account.

Terminoloji

Alternatif adlar ve kullanım biçimleri

Signed comparison

The "signed comparison" term is often used to describe when the product uses a signed variable and checks it to ensure that it is less than a maximum value (typically a maximum buffer size), but does not verify that it is greater than 0.

Kök neden

Problem nasıl ve ne zaman oluşur?

Yaşam döngüsü evresi

Implementation

Risk

Başarılı sömürü neye yol açar?

Modify Application DataExecute Unauthorized Code or Commands

Etkilenen güvenlik alanları: Integrity, Confidentiality, Availability

An attacker could modify the structure of the message or data being sent to the downstream component, possibly injecting commands.
DoS: Resource Consumption (Other)

Etkilenen güvenlik alanları: Availability

in some contexts, a negative value could lead to resource consumption.
Modify MemoryRead Memory

Etkilenen güvenlik alanları: Confidentiality, Integrity

If a negative value is used to access memory, buffers, or other indexable structures, it could access memory outside the bounds of the buffer.

Savunma

Nasıl önlenir ve çözülür?

Implementation

Enforcement by Conversion

Detay
If the number to be used is always expected to be positive, change the variable type from signed to unsigned or size_t.

Implementation

Input Validation

Detay
If the number to be used could have a negative value based on the specification (thus requiring a signed value), but the number should only be positive to preserve code correctness, then include a check to ensure that the value is positive.

Doğrulama

Nasıl tespit edilir?

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.)