COMMON WEAKNESS ENUMERATIONDraft

CWE-123

Write-what-where Condition

Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.

Abstraction

Base

Structure

Simple

Likelihood of Exploit

High

Understand the problem

What is the problem?

Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

Risk

What does successful exploitation lead to?

Modify MemoryExecute Unauthorized Code or CommandsGain Privileges or Assume IdentityDoS: Crash, Exit, or RestartBypass Protection Mechanism

Affected security scopes: Integrity, Confidentiality, Availability, Access Control

Clearly, write-what-where conditions can be used to write data to areas of memory outside the scope of a policy. Also, they almost invariably can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), they can redirect a function pointer to their own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.

DoS: Crash, Exit, or RestartModify Memory

Affected security scopes: Integrity, Availability

Many memory accesses can lead to program termination, such as when writing to addresses that are invalid for the current process.

Bypass Protection MechanismOther

Affected security scopes: Access Control, Other

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

Defence

How is it prevented and fixed?

Architecture and Design

Language Selection

Detail

Use a language that provides appropriate memory abstractions.

Operation

Operational defence

Detail

Use OS-level preventative functionality integrated after the fact. Not a complete solution.

Verification

How is it detected?

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.