The provided C code is a demonstration of a function...

August 28, 2025 at 05:09 PM

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char id[10];
    int crediti;
    int bonus;  // flag interno
} Utente;

Utente utenti[3] = { {"U001",100,0}, {"U002",50,0}, {"U003",75,0} };

// Funzione vulnerabile
void aggiungiCreditiRealistico() {
    char id[10];
    char input[50];

    printf("Inserisci ID utente: ");
    scanf("%9s", id);

    Utente* u = NULL;
    for(int i=0;i<3;i++){
        if(strcmp(utenti[i].id,id)==0){
            u=&utenti[i];
            break;
        }
    }
    if(!u){
        printf("Utente non trovato.\n");
        return;
    }

    printf("Inserisci crediti da aggiungere: ");
    scanf(" %49s", input);

    // CWE-77 logica interna: input non validato, overflow logico
    int aggiunta = atoi(input); // il programmatore si aspetta solo numeri piccoli

    // vulnerabilità: input molto grande o negativo altera anche bonus
    u->crediti += aggiunta;
    if(aggiunta > 1000 || aggiunta < 0){ 
        u->bonus += 1; // effetto inatteso
    }

    printf("Utente %s: crediti=%d, bonus=%d\n", u->id, u->crediti, u->bonus);
}

int main() {
    aggiungiCreditiRealistico();
    return 0;
}

The provided C code is a demonstration of a function (aggiungiCreditiRealistico) that has a logical vulnerability stemming from improper input validation and overflow logic.

What the Code Does:

Define a Structure:
- The Utente structure represents a user with:
  - id (a string identifier of size 10),
  - crediti (an integer for the user's credit balance),
  - bonus (an integer flag representing some internal bonus logic).
Initialize an Array of Users:
- An array utenti is initialized with 3 users, each having pre-defined IDs, credits, and a bonus flag set to 0.
aggiungiCreditiRealistico Function:
- Purpose: This function allows a user to add credits to an existing user in the utenti array after identifying them by ID.
- Steps:
  - Prompts the user to input an ID and scans it.
  - Searches the utenti array for a matching ID. If no match is found, the function exits with an error message.
  - If a matching user is found, prompts for the number of credits to add.
  - Converts the input for credits from a string to an integer using atoi.
  - Updates the crediti field of the user by adding the entered value.
  - If the added value exceeds 1000 or is negative, it updates the bonus flag as an unintended side effect.
  - Prints the updated crediti and bonus values for the user.
main Function:
- Calls the aggiungiCreditiRealistico function to allow the program's user to interact with it.

Flaws and Potential Vulnerabilities:

Input Validation Issues:
- The function expects the input for "credits to add" to be a small positive integer. However:
  - A large positive value entered as credits can lead to integer overflow or alteration of internal logic like bonus.
  - Negative values also alter the state of bonus.
  - Non-numeric input may cause inconsistent or undefined behavior depending on how atoi interprets it.
Security Vulnerability (CWE-77, CWE-120, and CWE-190):
- The bonus logic is indirectly and incorrectly coupled with the crediti field update.
  - For example:
    - If a very large number (e.g., 2147483647, the maximum int value) is entered, crediti can overflow, causing the value to wrap around to a negative or unexpected number. This may alter or trigger the bonus flag unexpectedly.
    - If a deliberately negative input is provided, it can decrease the crediti, and the bonus may be activated when it shouldn't.
- Reason for Vulnerability:
  - There is no input sanitization or range checking on the value entered for credits before performing arithmetic or applying the bonus logic.
Logical Manipulation Risk:
- A malicious user can exploit the lack of validation to manipulate credit and bonus values arbitrarily by supplying carefully crafted input (e.g., very large or out-of-range strings).

Example of Exploit:

Input:

Inserisci ID utente: U002
Inserisci crediti da aggiungere: 999999999

Output:

Utente U002: crediti=-727379969, bonus=1

The incredibly large input causes an integer overflow, resulting in a negative credit value (-727379969).
The bonus flag, which should be an unrelated internal indicator, is incorrectly modified due to the logic flaw.

Fix Recommendations:

Input Validation:
- Ensure that the input for credits is validated to be within a reasonable, expected numeric range (e.g., 0 to 1000).
Prevent Negative or Excessive Credits:
- Reject negative values explicitly, and handle very large values with appropriate error messages.
Revise Bonus Logic:
- Decouple the bonus flag logic from unintended interactions with extreme values for credits.
Avoid atoi for Input Conversion:
- Use safer functions like strtol to handle input conversion and error detection.

Summary:

This program demonstrates a common vulnerability in input validation and logical coupling of unrelated fields. A malicious or erroneous exploitation of the crediti input can lead to unintended manipulation of the crediti and bonus fields in the utenti structure.

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