Vulnerable code sample

import secrets
import hashlib

# WARNING: This code demonstrates a vulnerability (CVE-2025-29779)
# and should NOT be used in production. It is for educational purposes only.

class VSS:
    def __init__(self, t, n, p, g):
        """
        t: threshold
        n: number of shares
        p: large prime
        g: generator
        """
        self.t = t
        self.n = n
        self.p = p
        self.g = g

    def generate_polynomial(self):
        """Generates random polynomial coefficients."""
        coeffs = [secrets.randbelow(self.p) for _ in range(self.t)]
        return coeffs

    def evaluate_polynomial(self, x, coeffs):
        """Evaluates the polynomial at a given point x."""
        y = 0
        for i, coeff in enumerate(coeffs):
            y = (y + coeff * pow(x, i, self.p)) % self.p
        return y

    def generate_shares(self, secret):
        """Generates shares of the secret."""
        coeffs = [secret] + self.generate_polynomial()[1:] #Secret is the first coefficient
        shares = []
        for i in range(1, self.n + 1):
            x = i
            y = self.evaluate_polynomial(x, coeffs)
            shares.append((x, y))
        return shares, coeffs

    def verify_share(self, share, commitments):
        """Verifies a single share against the commitments."""
        x, y = share
        commitment_check = 0
        for i, commitment in enumerate(commitments):
            commitment_check = (commitment_check + commitment * pow(x, i, self.p)) % self.p

        expected_commitment = pow(self.g, y, self.p)
        return commitment_check == expected_commitment

    def generate_commitments(self, coeffs):
        """Generates commitments to the polynomial coefficients."""
        commitments = []
        for coeff in coeffs:
            commitments.append(pow(self.g, coeff, self.p))
        return commitments

    def reconstruct_secret(self, shares):
        """Reconstructs the secret from a subset of shares."""
        if len(shares) < self.t:
            raise ValueError("Not enough shares to reconstruct the secret.")

        x_values = [share[0] for share in shares]
        y_values = [share[1] for share in shares]

        secret = 0
        for i in range(len(shares)):
            numerator = 1
            denominator = 1
            for j in range(len(shares)):
                if i != j:
                    numerator = (numerator * (-x_values[j])) % self.p
                    denominator = (denominator * (x_values[i] - x_values[j])) % self.p

            # Ensure denominator is invertible (not zero)
            if denominator == 0:
                raise ValueError("Shares are not distinct.")

            lagrange_basis = (numerator * pow(denominator, self.p - 2, self.p)) % self.p # Fermat's Little Theorem

            secret = (secret + y_values[i] * lagrange_basis) % self.p

        return secret

    def secure_redundant_execution(self, func, *args): # Vulnerable function
        """
        Executes a function multiple times and compares results to mitigate fault injection attacks.

        This function is vulnerable to CVE-2025-29779.
        """
        num_executions = 5
        results = []
        for _ in range(num_executions):
            results.append(func(*args))

        # Constant-time comparison (attempt)
        first_result = results[0]
        for result in results[1:]:
            if not self.constant_time_compare(first_result, result):
                raise ValueError("Inconsistent execution results detected!")
        return first_result

    def constant_time_compare(self, val1, val2): #Vulnerable
        """
        Attempts to compare two values in constant time to prevent timing attacks.

        This function is vulnerable to CVE-2025-29779 due to Python's lack of true isolation.
        """
        if isinstance(val1, bytes) and isinstance(val2, bytes):
            if len(val1) != len(val2):
                return False
            result = 0
            for x, y in zip(val1, val2):
                result |= x ^ y
            return result == 0
        else:
            # In real code, constant time comparison would be implemented at the bit level
            # Python integer comparison is not constant time
            return val1 == val2

# Example usage demonstrating potential vulnerability

if __name__ == '__main__':
    # Example parameters (use a large prime for real applications)
    t = 3  # Threshold
    n = 5  # Number of shares
    p = 101  # Small prime for demonstration purposes
    g = 2  # Generator

    vss = VSS(t, n, p, g)
    secret = 42
    shares, coeffs = vss.secure_redundant_execution(vss.generate_shares, secret)  #Applying Redundant Execution
    commitments = vss.secure_redundant_execution(vss.generate_commitments, coeffs)  #Applying Redundant Execution


    # Verify shares
    valid_shares = []
    for share in shares:
        is_valid = vss.secure_redundant_execution(vss.verify_share, share, commitments)  #Applying Redundant Execution
        if is_valid:
            valid_shares.append(share)
        else:
            print(f"Share {share} is invalid.")

    # Reconstruct secret from a subset of valid shares
    try:
        reconstruction_shares = valid_shares[:t]  #Use t shares for reconstruction
        reconstructed_secret = vss.secure_redundant_execution(vss.reconstruct_secret, reconstruction_shares)  #Applying Redundant Execution
        print(f"Reconstructed secret: {reconstructed_secret}")

        if reconstructed_secret == secret:
            print("Secret successfully reconstructed!")
        else:
            print("Secret reconstruction failed.")

    except ValueError as e:
        print(f"Error during secret reconstruction: {e}")