Compiler Removal of Code to Clear Buffers

Sensitive memory is cleared according to the source code, but compiler optimizations leave the memory untouched when it is not read from again, aka "dead store removal."


This compiler optimization error occurs when:

Secret data are stored in memory.

The secret data are scrubbed from memory by overwriting its contents.

The source code is compiled using an optimizing compiler, which identifies and removes the function that overwrites the contents as a dead store because the memory is not used subsequently.


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 reads a password from the user, uses the password to connect to a back-end mainframe and then attempts to scrub the password from memory using memset().

void GetData(char *MFAddr) {

  char pwd[64];
  if (GetPasswordFromUser(pwd, sizeof(pwd))) {

    if (ConnectToMainframe(MFAddr, pwd)) {

      // Interaction with mainframe


  memset(pwd, 0, sizeof(pwd));


The code in the example will behave correctly if it is executed verbatim, but if the code is compiled using an optimizing compiler, such as Microsoft Visual C++ .NET or GCC 3.x, then the call to memset() will be removed as a dead store because the buffer pwd is not used after its value is overwritten [18]. Because the buffer pwd contains a sensitive value, the application may be vulnerable to attack if the data are left memory resident. If attackers are able to access the correct region of memory, they may use the recovered password to gain control of the system.

It is common practice to overwrite sensitive data manipulated in memory, such as passwords or cryptographic keys, in order to prevent attackers from learning system secrets. However, with the advent of optimizing compilers, programs do not always behave as their source code alone would suggest. In the example, the compiler interprets the call to memset() as dead code because the memory being written to is not subsequently used, despite the fact that there is clearly a security motivation for the operation to occur. The problem here is that many compilers, and in fact many programming languages, do not take this and other security concerns into consideration in their efforts to improve efficiency.

Attackers typically exploit this type of vulnerability by using a core dump or runtime mechanism to access the memory used by a particular application and recover the secret information. Once an attacker has access to the secret information, it is relatively straightforward to further exploit the system and possibly compromise other resources with which the application interacts.

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 49 - Miscellaneous (MSC)

Weaknesses in this category are related to rules in the Miscellaneous (MSC) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific weaknes...

7PK - Environment

This category represents one of the phyla in the Seven Pernicious Kingdoms vulnerability classification. It includes weaknesses that are typically introduced during un...

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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