Improper Clearing of Heap Memory Before Release ('Heap Inspection')

Using realloc() to resize buffers that store sensitive information can leave the sensitive information exposed to attack, because it is not removed from memory.


When sensitive data such as a password or an encryption key is not removed from memory, it could be exposed to an attacker using a "heap inspection" attack that reads the sensitive data using memory dumps or other methods. The realloc() function is commonly used to increase the size of a block of allocated memory. This operation often requires copying the contents of the old memory block into a new and larger block. This operation leaves the contents of the original block intact but inaccessible to the program, preventing the program from being able to scrub sensitive data from memory. If an attacker can later examine the contents of a memory dump, the sensitive data could be exposed.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following code calls realloc() on a buffer containing sensitive data:

cleartext_buffer = get_secret();...
cleartext_buffer = realloc(cleartext_buffer, 1024);
scrub_memory(cleartext_buffer, 1024);

There is an attempt to scrub the sensitive data from memory, but realloc() is used, so a copy of the data can still be exposed in the memory originally allocated for cleartext_buffer.

See Also

SFP Secondary Cluster: Exposed Data

This category identifies Software Fault Patterns (SFPs) within the Exposed Data cluster (SFP23).

CERT C++ Secure Coding Section 08 - Memory Management (MEM)

Weaknesses in this category are related to rules in the Memory Management (MEM) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific wea...

7PK - API Abuse

This category represents one of the phyla in the Seven Pernicious Kingdoms vulnerability classification. It includes weaknesses that involve the software using an API ...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

CWE Cross-section

This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

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