ENV01-A. Do not make assumptions about the size of an environment variable

Do not make any assumptions about the size of environment variables, as an adversary could have full control over the environment. Calculate the length of the strings yourself, and dynamically allocate memory for your copies [STR31-C].

Non-Compliant Code Example

This non-compliant code example copies the string returned by getenv() into a fixed size buffer. This can result in a buffer overflow.

char *temp;
char copy[16];

temp = getenv("TEST_ENV");
if (temp != NULL) {
  strcpy(buff, temp);
}

Compliant Solution

Use the strlen() function to calculate the size of the string and dynamically allocate the required space.

char *temp;
char *copy = NULL;

if ((temp = getenv("TEST_ENV")) != NULL) {
  copy = malloc(strlen(temp) + 1);
  if (copy != NULL) {
    strcpy(copy, temp);
  }
  else {
    /* handle error condition */
  }
}

Risk Assessment

Making assumptions about the size of an environmental variable could result in a buffer overflow attack.

References

[[ISO/IEC 9899-1999:TC2]] Section 7.20.4, "Communication with the environment"
[[Open Group 04]] Chapter 8, "Environment Variables"
[[Viega 03]] Section 3.6, "Using Environment Variables Securely"