CWE-672: Operation on a Resource after Expiration or Release

Description

The product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.

Potential Impact

Integrity, Confidentiality

Modify Application Data, Read Application Data

Other, Availability

Other, DoS: Crash, Exit, or Restart

Demonstrative Examples

The following code shows a simple example of a use after free error:

Bad

char* ptr = (char*)malloc (SIZE);if (err) {abrt = 1;free(ptr);}...if (abrt) {logError("operation aborted before commit", ptr);}

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

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

Bad

char* ptr = (char*)malloc (SIZE);...if (abrt) {free(ptr);}...free(ptr);

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

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.

Bad

#define FAIL 0#define SUCCESS 1#define ERROR -1#define MAX_MESSAGE_SIZE 32
                     int processMessage(char **message){
                        int result = SUCCESS;
                           int length = getMessageLength(message[0]);char *messageBody;
                           if ((length > 0) && (length < MAX_MESSAGE_SIZE)) {
                           
                              messageBody = (char*)malloc(length*sizeof(char));messageBody = &message[1][0];
                                 int success = processMessageBody(messageBody);
                                 if (success == ERROR) {result = ERROR;free(messageBody);}
                           }else {printf("Unable to process message; invalid message length");result = FAIL;}
                           if (result == ERROR) {logError("Error processing message", messageBody);}
                           return result;
                     }

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.

Good

...messageBody = (char*)malloc(length*sizeof(char));messageBody = &message[1][0];
                     int success = processMessageBody(messageBody);
                     if (success == ERROR) {result = ERROR;logError("Error processing message", messageBody);free(messageBody);}...

Detection Methods

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 sea

Real-World CVE Examples

CVE ID	Description
CVE-2009-3547	Chain: race condition (CWE-362) might allow resource to be released before operating on it, leading to NULL dereference (CWE-476)

Taxonomy Mappings

Software Fault Patterns: SFP15 — Faulty Resource Use
CERT C Secure Coding: FIO46-C — Do not access a closed file
CERT C Secure Coding: MEM30-C — Do not access freed memory
OMG ASCSM: ASCSM-CWE-672 —

Frequently Asked Questions

What is CWE-672?

CWE-672 (Operation on a Resource after Expiration or Release) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. The product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.

How can CWE-672 be exploited?

Attackers can exploit CWE-672 (Operation on a Resource after Expiration or Release) to modify application data, read application data. This weakness is typically introduced during the Implementation, Operation phase of software development.

How do I prevent CWE-672?

Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.

What is the severity of CWE-672?

CWE-672 is classified as a Class-level weakness (High abstraction). It has been observed in 1 real-world CVEs.