This C code defines a small program that manages a...

This C code defines a small program that manages a fixed array of user objects and allows incrementing their "crediti" (credits) through a potentially vulnerable function. Here's the breakdown of what each part of the code does:

1. Data Structures and Initialization

typedef struct {
    char id[10];
    int crediti;
} Utente;

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

• A Utente structure is defined, which contains two fields:
  • id: A string representing the user ID (maximum of 9 characters + null terminator).
  • crediti: An integer representing the user's credits.
• An array utenti is initialized with three Utente objects representing users with predefined IDs and credits.

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2. The aggiungiCrediti Function

This function allows a user to update the credits for a specific user in the system. However, it contains a vulnerability due to improper input validation.

void aggiungiCrediti() {
    char id[10];
    char input[50];
    printf("Inserisci ID utente: ");
    scanf("%9s", id);

• Prompts the user to input a user ID (up to 9 characters).
• The program uses this ID to search for a matching user in the utenti array.

    Utente* u = NULL;
    for(int i=0;i<3;i++){
        if(strcmp(utenti[i].id,id)==0){ u=&utenti[i]; break; }
    }

• Searches the utenti array for a user with a matching ID.
• If found, a pointer u is set to the corresponding user object; otherwise, u remains NULL.

    if(!u){ 
        printf("Utente non trovato.\n"); 
        return; 
    }

• If the user ID is not found, the function exits with an error message.

    printf("Inserisci crediti da aggiungere: ");
    scanf(" %49[^\n]", input);

• Prompts the user to input a string (input) representing the number of credits to add.
• The input can hold up to 49 characters.

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3. Vulnerability: Improper Input Handling

    int aggiunta = 0;
    if(sscanf(input,"%d",&aggiunta)==1){
        u->crediti += aggiunta;
    } else {
        // esempio di vulnerabilità: input "10+20" viene valutato come 30
        aggiunta = atoi(strtok(input,"+")) + atoi(strtok(NULL,"+"));
        u->crediti += aggiunta;
    }

• The function attempts to interpret the input string as an integer using sscanf.
• If sscanf fails (e.g., non-numeric input), the program falls back to a naive parsing mechanism to handle non-standard input like "10+20".
  • strtok splits the input string by the '+' character.
  • The program converts the resulting "tokens" into integers using atoi and performs a manual addition of the two numbers.
• This input parsing method enables vulnerable behavior:
  • An attacker could exploit this logic to input non-standard, partially valid, or malicious data (e.g., "10+20") to bypass normal formatting.

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4. Output and Results

    printf("Utente %s ha ora %d crediti\n", u->id, u->crediti);

• Displays the updated credits for the target user.

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5. Main Function

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

• Calls the aggiungiCrediti function to interactively add credits to a user.

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Vulnerabilities in the Code

The code contains the following security and functionality issues:

1. Improper Input Validation:

   • When parsing input, the code does not validate or sanitize it properly. For example, input like 10+20 will be accepted and processed as 30 credits.
   • Malformed or malicious inputs can cause undefined behavior depending on how strtok and atoi interpret them.

2. Arithmetic Parsing:

   • The fallback mechanism in aggiungiCrediti allows basic arithmetic expressions like "10+20" but fails to handle more complex cases or invalid input robustly.
   • Exploiting this logic, users might even inject unexpected values.

3. Limited User Search:

   • Only three users are hardcoded in memory. Additional inputs or scalability are not handled.
   • Related edge cases (e.g., extremely large input or buffer overflows) can lead to crashes.

4. Lack of Input Sanitization:

   • The program assumes inputs are well-formed and does not check for overflow, underflow, or invalid characters.

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Example Vulnerable Behavior

Case 1: Regular input

Input:

Inserisci ID utente: U001
Inserisci crediti da aggiungere: 25

Output:

Utente U001 ha ora 125 crediti

Case 2: Exploiting Arithmetic Parsing

Input:

Inserisci ID utente: U002
Inserisci crediti da aggiungere: 10+20

Output:

Utente U002 ha ora 80 crediti

Case 3: Malformed Input (Potential Crash or Incorrect Behavior)

Input:

Inserisci ID utente: U003
Inserisci crediti da aggiungere: 5++10---20

Behavior:

• May result in undefined behavior or incorrect parsing.
• The program might crash or process a random "crediti" value due to improper handling.

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Summary

This code implements a simple user credit system with a vulnerable aggiungiCrediti function. The vulnerability arises from poor input validation and naive arithmetic parsing, which attackers can exploit to manipulate or crash the program.