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Difference between revisions of "Doubly freeing memory"

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Last revision (mm/dd/yy): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''
 
[[ASDR_TOC_Vulnerabilities|Vulnerabilities Table of Contents]]
 
  
 
==Description==
 
==Description==
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Doubly freeing memory can result in roughly the same write-what-where condition that the use of previously freed memory will.  
 
Doubly freeing memory can result in roughly the same write-what-where condition that the use of previously freed memory will.  
 
 
==Risk Factors==
 
 
TBD
 
  
 
==Examples==
 
==Examples==
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==Related [[Attacks]]==
 
* [[Attack 1]]
 
* [[Attack 2]]
 
 
 
==Related [[Vulnerabilities]]==
 
* [[Using freed memory]]
 
* [[Write-what-where condition]]
 
 
  
 
==Related [[Controls]]==
 
==Related [[Controls]]==
* Implementation: Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
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* Implementation: Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
 
 
 
 
==Related [[Technical Impacts]]==
 
* [[Technical Impact 1]]
 
* [[Technical Impact 2]]
 
 
 
 
 
==References==
 
TBD
 
 
 
[[Category:FIXME|add links
 
 
 
In addition, one should classify vulnerability based on the following subcategories: Ex:<nowiki>[[Category:Error Handling Vulnerability]]</nowiki>
 
 
 
Availability Vulnerability
 
 
 
Authorization Vulnerability
 
 
 
Authentication Vulnerability
 
 
 
Concurrency Vulnerability
 
 
 
Configuration Vulnerability
 
 
 
Cryptographic Vulnerability
 
 
 
Encoding Vulnerability
 
 
 
Error Handling Vulnerability
 
 
 
Input Validation Vulnerability
 
 
 
Logging and Auditing Vulnerability
 
 
 
Session Management Vulnerability]]
 
  
 
__NOTOC__
 
__NOTOC__
  
 
[[Category:OWASP ASDR Project]]
 
 
[[Category:Vulnerability]]
 
[[Category:Vulnerability]]
[[Category:Range and Type Error Vulnerability]]
 
[[Category:OWASP_CLASP_Project]]
 
[[Category:Code Snippet]]
 
 
[[Category:C/C++]]
 
[[Category:C/C++]]
[[Category:Implementation]]
 

Revision as of 21:36, 28 July 2016

This is a Vulnerability. To view all vulnerabilities, please see the Vulnerability Category page.


Last revision (mm/dd/yy): 07/28/2016

Description

Freeing or deleting the same memory chunk twice may - when combined with other flaws - result in a write-what-where condition.

Consequences

  • Access control: Doubly freeing memory may result in a write-what-where condition, allowing an attacker to execute arbitrary code.

Exposure period

  • Requirements specification: A language which handles memory allocation and garbage collection automatically might be chosen.
  • Implementation: Double frees are caused most often by lower-level logical errors.

Platform

  • Language: C, C++, Assembly
  • Operating system: All

Required resources

Any

Severity

High

Likelihood of exploit

Low to Medium

Doubly freeing memory can result in roughly the same write-what-where condition that the use of previously freed memory will.

Examples

While contrived, this code should be exploitable on Linux distributions which do not ship with heap-chunk check summing turned on.

#include <stdio.h>
#include <unistd.h>

#define BUFSIZE1    512
#define BUFSIZE2    ((BUFSIZE1/2) - 8)

int main(int argc, char **argv) { 
  char *buf1R1;    
  char *buf2R1;    
  char *buf1R2;    

  buf1R1 = (char *) malloc(BUFSIZE2);    
  buf2R1 = (char *) malloc(BUFSIZE2);    
  
  free(buf1R1);    
  free(buf2R1);    

  buf1R2 = (char *) malloc(BUFSIZE1);    
  strncpy(buf1R2, argv[1], BUFSIZE1-1);    
  
  free(buf2R1);    
  free(buf1R2);
}

Related Controls

  • Implementation: Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.