SV.UNBOUND_STRING_INPUT.FUNC
Buffer overflow from unbounded string copy
The string copy function is used to copy a string of characters to a buffer of memory. The strcpy function has no argument to limit the size of the written data, so a buffer overflow may result.
The SV.UNBOUNDED_STRING_INPUT.FUNC checker looks for code calling insecure string copy functions that don't specify a buffer size, like gets(), gettext(), or catgets().
Vulnerability and risk
If the string copy function is called without a size parameter, a buffer overrun error can result. This can lead to application instability or, with a carefully constructed attack, code injection, or other vulnerabilities.
Mitigation and prevention
To avoid this vulnerability
- make sure you use functions that have buffer size as an input parameter, like fgets instead of gets
- for Windows, use StrSafe functions String*Gets, such as StringCchGets, or Safe CRT functions like gets_s
- use a function like strlen() to determine the buffer size you need
Vulnerable code example 1
Copy
#include <stdio.h>
int main()
{
char string [256];
printf ("Insert your full address: ");
gets (string); /* SV.UNBOUND_STRING_INPUT.FUNC reported here */
printf ("Your address is: %s\n",string);
return 0;
}Fixed code example 1
Copy
#include <stdio.h>
int main()
{
char string [256];
printf ("Insert your full address: ");
fgets (string, 256, stdin); /* No checker reported because fgets considers the size of the string array */
printf ("Your address is: %s\n",string);
return 0;
}Vulnerable code example 2
Copy
#include <stdio.h>
int main()
{
char string [256];
printf ("Please Enter Your Full Name:");
_gettws (string); /* SV.UNBOUND_STRING_INPUT.FUNC reported here */
printf ("Your Full Name Is: %s\n", string);
return 0;
}Fixed code example 2
Copy
#include <stdio.h>
int main()
{
char string [256];
printf ("Please Enter Your Full Name:");
gets_s (string, strlen(string)); /* no SV.UNBOUND_STRING_INPUT.FUNC reported here */
printf ("Your Full Name Is: %s\n", string);
return 0;
}Related checkers
External guidance
- CERT STR31-C: Guarantee that storage for strings has sufficient space for character data and the null terminator
- CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
- CWE-120: Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- CWE-125: Out-of-bounds Read
- CWE-242: Use of Inherently Dangerous Function
- CWE-787: Out-of-bounds Write
- STIG-ID:APP3590.2 Application is vulnerable to buffer overflows
Security training
Application security training materials provided by Secure Code Warrior.