Use After Free

Stable Variant

Structure: Simple

Description

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 Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Common Consequences 3

Scope: Integrity

Impact: Modify Memory

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

Scope: Availability

Impact: DoS: Crash, Exit, or Restart

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

Scope: IntegrityConfidentialityAvailability

Impact: Execute Unauthorized Code or Commands

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.

Detection Methods 2

FuzzingHigh

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 AnalysisHigh

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.)

Potential Mitigations 2

Phase: Architecture and Design

Strategy: Language Selection

Choose a language that provides automatic memory management.

Phase: Implementation

Strategy: Attack Surface Reduction

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

Demonstrative Examples 2

The following example demonstrates the weakness.

Code Example:Bad
C
c

The following code illustrates a use after free error:

Code Example:Bad
C
c

When an error occurs, the pointer is immediately freed. However, this pointer is later incorrectly used in the logError function.

Observed Examples 28

CVE-2022-20141Chain: an operating system kernel has insufficent resource locking (Improper Resource Locking) leading to a use after free (Use After Free).

CVE-2022-2621Chain: two threads in a web browser use the same resource (Race Condition within a Thread), but one of those threads can destroy the resource before the other has completed (Use After Free).

CVE-2021-0920Chain: mobile platform race condition (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) leading to use-after-free (Use After Free), as exploited in the wild per CISA KEV.

CVE-2020-6819Chain: race condition (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) leads to use-after-free (Use After Free), as exploited in the wild per CISA KEV.

CVE-2010-4168Use-after-free triggered by closing a connection while data is still being transmitted.

CVE-2010-2941Improper allocation for invalid data leads to use-after-free.

CVE-2010-2547certificate with a large number of Subject Alternate Names not properly handled in realloc, leading to use-after-free

CVE-2010-1772Timers are not disabled when a related object is deleted

CVE-2010-1437Access to a "dead" object that is being cleaned up

CVE-2010-1208object is deleted even with a non-zero reference count, and later accessed

CVE-2010-0629use-after-free involving request containing an invalid version number

CVE-2010-0378unload of an object that is currently being accessed by other functionality

CVE-2010-0302incorrectly tracking a reference count leads to use-after-free

CVE-2010-0249use-after-free related to use of uninitialized memory

CVE-2010-0050HTML document with incorrectly-nested tags

CVE-2009-3658Use after free in ActiveX object by providing a malformed argument to a method

CVE-2009-3616use-after-free by disconnecting during data transfer, or a message containing incorrect data types

CVE-2009-3553disconnect during a large data transfer causes incorrect reference count, leading to use-after-free

CVE-2009-2416use-after-free found by fuzzing

CVE-2009-1837Chain: race condition (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) from improper handling of a page transition in web client while an applet is loading (Context Switching Race Condition) leads to use after free (Use After Free)

CVE-2009-0749realloc generates new buffer and pointer, but previous pointer is still retained, leading to use after free

CVE-2010-3328Use-after-free in web browser, probably resultant from not initializing memory.

CVE-2008-5038use-after-free when one thread accessed memory that was freed by another thread

CVE-2008-0077assignment of malformed values to certain properties triggers use after free

CVE-2006-4434mail server does not properly handle a long header.

CVE-2010-2753chain: integer overflow leads to use-after-free

CVE-2006-4997freed pointer dereference

CVE-2003-0813Chain: A multi-threaded race condition (Time-of-check Time-of-use (TOCTOU) Race Condition) allows attackers to cause two threads to process the same RPC request, which causes a use-after-free (Use After Free) in one thread

References 3

Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors

Katrina Tsipenyuk, Brian Chess, and Gary McGraw

NIST Workshop on Software Security Assurance Tools Techniques and Metrics • NIST

07-11-2005

https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf

ID: REF-6

The CLASP Application Security Process

Secure Software, Inc.

2005

https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)

ID: REF-18

24 Deadly Sins of Software Security

Michael Howard, David LeBlanc, and John Viega

McGraw-Hill

2010

ID: REF-44

Likelihood of Exploit

High

Applicable Platforms

Languages:

C : UndeterminedC++ : Undetermined

Modes of Introduction

Implementation

Alternate Terms

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

Functional Areas

Memory Management

Affected Resources

Memory

Related Weaknesses

ChildOf:

Expired Pointer Dereference (CWE-825)

ChildOf:

Operation on a Resource after Expiration or Release (CWE-672)

ChildOf:

Operation on a Resource after Expiration or Release (CWE-672)

ChildOf:

Operation on a Resource after Expiration or Release (CWE-672)

CanPrecede:

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') (CWE-120)

CanPrecede:

Write-what-where Condition (CWE-123)

Taxonomy Mapping

ISA/IEC 62443
7 Pernicious Kingdoms
CLASP
CERT C Secure Coding
CERT C Secure Coding
CERT C Secure Coding
Software Fault Patterns