CWE Rule 316

Cleartext Storage of Sensitive Information in Memory

Since R2024a

Description

Rule Description

The product stores sensitive information in cleartext in memory.

Polyspace Implementation

The rule checker checks for these issues:

• Sensitive heap memory not cleared before release

• Uncleared sensitive data in stack

Examples

Sensitive heap memory not cleared before release

Issue

This issue occurs when dynamically allocated memory contains sensitive data and you do not clear the data before you free the memory.

Risk

If the memory zone is reallocated, an attacker can still inspect the sensitive data in the old memory zone.

Fix

Before calling free, clear out the sensitive data using memset or SecureZeroMemory.

Example — Sensitive Buffer Freed, Not Cleared

#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>

void sensitiveheapnotcleared(const char * my_user) {
    struct passwd* result, pwd;
    long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
    char* buf = (char*) malloc(1024);
    getpwnam_r(my_user, &pwd, buf, bufsize, &result);
    free(buf); //Noncompliant
}

In this example, the function uses a buffer of passwords and frees the memory before the end of the function. However, the data in the memory is not cleared by using the free command.

Correction — Nullify Data

One possible correction is to write over the data to clear out the sensitive information. This example uses memset to write over the data with zeros.

#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <assert.h>

#define isNull(arr) for(int i=0;i<(sizeof(arr)/sizeof(arr[0]));i++) assert(arr[i]==0)

void sensitiveheapnotcleared(const char * my_user) {
    struct passwd* result, pwd;
    long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
    char* buf = (char*) malloc(1024);

    if (buf) {
        getpwnam_r(my_user, &pwd, buf, bufsize, &result);
        memset(buf, 0, (size_t)1024);
        isNull(buf);
        free(buf); 
    }
}

Uncleared sensitive data in stack

Issue

This issue occurs when statically allocated memory contains sensitive data and you do not clear the data before exiting a function or program.

Risk

Leaving sensitive information in your stack, such as passwords or user information, allows an attacker additional access to the information after your program has ended.

Fix

Before exiting a function or program, clear out the memory zones that contain sensitive data by using memset or SecureZeroMemory.

Example — Static Buffer of Password Information

#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>

void bug_sensitivestacknotcleared(const char * my_user) {
    struct passwd* result, pwd;
    long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
    char buf[1024] = "";
    getpwnam_r(my_user, &pwd, buf, bufsize, &result);
}  //Noncompliant

In this example, a static buffer is filled with password information. The program frees the stack memory at the end of the program. However, the data is still accessible from the memory.

Correction — Clear Memory

One possible correction is to write over the memory before exiting the function. This example uses memset to clear the data from the buffer memory.

#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <assert.h>

#define isNull(arr) for(int i=0;i<(sizeof(arr)/sizeof(arr[0]));i++) assert(arr[i]==0)

void corrected_sensitivestacknotcleared(const char * my_user) {
    struct passwd* result, pwd;
    long bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
    char buf[1024] = "";
    getpwnam_r(my_user, &pwd, buf, bufsize, &result);
    memset(buf, 0, (size_t)1024);
    isNull(buf);
}

Check Information

Category: Others

Version History

Introduced in R2024a