CWE Rule 127

Buffer Under-read

Since R2023a

Description

The software reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations prior to the targeted buffer.

Polyspace Implementation

The rule checker checks for Buffer overflow from incorrect string format specifier.

Examples

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Buffer overflow from incorrect string format specifier

Issue

This issue occurs when the format specifier argument for functions such as sscanf leads to an overflow or underflow in the memory buffer argument.

Risk

If the format specifier specifies a precision that is greater than the memory buffer size, an overflow occurs. Overflows can cause unexpected behavior such as memory corruption.

Fix

Use a format specifier that is compatible with the memory buffer size.

Example — Memory Buffer Overflow

#include <stdio.h>

void func (char *str[]) {
    char buf[32];
    sscanf(str[1], "%33c", buf);  //Noncompliant
}

In this example, buf can contain 32 char elements. Therefore, the format specifier %33c causes a buffer overflow.

Correction — Use Smaller Precision in Format Specifier

One possible correction is to read a smaller number of elements into the buffer.

#include <stdio.h>

void func (char *str[]) {
    char buf[32];
    sscanf(str[1], "%32c", buf);
}

Check Information

Category: Others

PQL Name: std.cwe_native.R127

Version History

Introduced in R2023a