COMMON WEAKNESS ENUMERATIONIncomplete

CWE-124

Buffer Underwrite ('Buffer Underflow')

The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.

Soyutlama

Base

Yapı

Simple

Sömürü İhtimali

Medium

Problemi anla

Problem nedir?

The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.

Terminoloji

Alternatif adlar ve kullanım biçimleri

buffer underrun

Some prominent vendors and researchers use the term "buffer underrun". "Buffer underflow" is more commonly used, although both terms are also sometimes used to describe a buffer under-read (CWE-127).

Kök neden

Problem nasıl ve ne zaman oluşur?

Yaşam döngüsü evresi

Implementation

This typically occurs when a pointer or its index is decremented to a position before the buffer, when pointer arithmetic results in a position before the beginning of the valid memory location, or when a negative index is used.

Risk

Başarılı sömürü neye yol açar?

Modify MemoryDoS: Crash, Exit, or Restart

Etkilenen güvenlik alanları: Integrity, Availability

Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.
Execute Unauthorized Code or CommandsModify MemoryBypass Protection MechanismOther

Etkilenen güvenlik alanları: Integrity, Confidentiality, Availability, Access Control, Other

If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy. The consequences would only be limited by how the affected data is used, such as an adjacent memory location that is used to specify whether the user has special privileges.
Bypass Protection MechanismOther

Etkilenen güvenlik alanları: Access Control, Other

When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

Savunma

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Requirements

Güvenlik gereksinimi

Detay
Choose a language that is not susceptible to these issues.

Implementation

Uygulama aşaması savunması

Detay
All calculated values that are used as index or for pointer arithmetic should be validated to ensure that they are within an expected range.

Doğrulama

Nasıl tespit edilir?

Automated Static Analysis

High
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.)

Automated Dynamic Analysis

Moderate
Use tools that are integrated during compilation to insert runtime error-checking mechanisms related to memory safety errors, such as AddressSanitizer (ASan) for C/C++ [REF-1518].

Crafted inputs are necessary to reach the code containing the error, such as generated by fuzzers. Also, these tools may reduce performance, and they only report the error condition - not the original mistake that led to the error.