COMMON WEAKNESS ENUMERATIONStable

CWE-416

Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Abstraction

Variant

Structure

Simple

Likelihood of Exploit

High

Understand the problem

What is the problem?

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Terminology

Alternate terms and usages

Dangling pointer

a pointer that no longer points to valid memory, often after it has been freed

UAF

commonly used acronym for Use After Free

Use-After-Free

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

Risk

What does successful exploitation lead to?

Modify Memory

Affected security scopes: Integrity

The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
DoS: Crash, Exit, or Restart

Affected security scopes: Availability

If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Read Memory

Affected security scopes: Confidentiality

Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Execute Unauthorized Code or Commands

Affected security scopes: Integrity, Confidentiality, Availability

If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Defence

How is it prevented and fixed?

Architecture and Design

Language Selection

Detail
Choose a language that provides automatic memory management.

Implementation

Attack Surface Reduction

Detail
When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

Effectiveness: Defense in Depth

If a bug causes an attempted access of this pointer, then a NULL dereference could still lead to a crash or other unexpected behavior, but it will reduce or eliminate the risk of code execution.

Verification

How is it detected?

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.

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.

MITRE diagram

Weakness relationships and flow

CWE-416 MITRE diagramı
CWE-416: Use After Free · DayBreach Sözlük · DayBreach