Operation on a Resource after Expiration or Release

Draft Class

Structure: Simple

Description

This vulnerability occurs when a program continues to use a resource—like memory, a file handle, or a network connection—after it has been freed, closed, or is no longer valid.

Extended Description

Think of this as using a hotel key card after you've checked out. The system has marked that resource as available for reuse, but your code still holds a reference to it. When you try to read, write, or execute operations using this 'stale' reference, the results are unpredictable. The program might crash, leak sensitive data from the now-reallocated memory, or allow an attacker to hijack the resource for their own purposes. To prevent this, developers must carefully manage the lifecycle of all resources. This means ensuring that every 'malloc' has a matching 'free', every 'open' has a 'close', and that pointers or handles are set to NULL or another invalid state immediately after release. Using modern language features like smart pointers in C++ or try-with-resources in Java can automate this cleanup and make these dangerous 'use-after-free' and 'use-after-close' errors much less likely.

Common Consequences 2

Scope: IntegrityConfidentiality

Impact: Modify Application DataRead Application Data

If a released resource is subsequently reused or reallocated, then an attempt to use the original resource might allow access to sensitive data that is associated with a different user or entity.

Scope: OtherAvailability

Impact: OtherDoS: Crash, Exit, or Restart

When a resource is released it might not be in an expected state, later attempts to access the resource may lead to resultant errors that may lead to a crash.

Demonstrative Examples 3

ID : DX-71

The following code shows a simple example of 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.

ID : DX-72

The following code shows a simple example of a double free error:

Code Example:Bad
C
c

Double free vulnerabilities have two common (and sometimes overlapping) causes:

- Error conditions and other exceptional circumstances - Confusion over which part of the program is responsible for freeing the memory

Although some double free vulnerabilities are not much more complicated than the previous example, most are spread out across hundreds of lines of code or even different files. Programmers seem particularly susceptible to freeing global variables more than once.

In the following C/C++ example the method processMessage is used to process a message received in the input array of char arrays. The input message array contains two char arrays: the first is the length of the message and the second is the body of the message. The length of the message is retrieved and used to allocate enough memory for a local char array, messageBody, to be created for the message body. The messageBody is processed in the method processMessageBody that will return an error if an error occurs while processing. If an error occurs then the return result variable is set to indicate an error and the messageBody char array memory is released using the method free and an error message is sent to the logError method.

Code Example:Bad
C
c

However, the call to the method logError includes the messageBody after the memory for messageBody has been released using the free method. This can cause unexpected results and may lead to system crashes. A variable should never be used after its memory resources have been released.

Code Example:Good
C
c

Observed Examples 1

CVE-2009-3547Chain: race condition (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')) might allow resource to be released before operating on it, leading to NULL dereference (NULL Pointer Dereference)

References 1

Automated Source Code Security Measure (ASCSM)

Object Management Group (OMG)

01-2016

http://www.omg.org/spec/ASCSM/1.0/

ID: REF-962

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Technologies:

Mobile : Undetermined

Modes of Introduction

Implementation

Operation

Related Weaknesses

ChildOf:

Operation on Resource in Wrong Phase of Lifetime (CWE-666)

Taxonomy Mapping

Software Fault Patterns
CERT C Secure Coding
CERT C Secure Coding
OMG ASCSM