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Unsafe standard encryption function

Function is not reentrant or uses a risky encryption algorithm

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Description

This defect occurs when a standard encryption function uses a broken or weak cryptographic algorithm. For example, crypt is not reentrant and is based on the risky Data Encryption Standard (DES).

Risk

The use of a broken, weak, or nonstandard algorithm can expose sensitive information to an attacker. A determined hacker can access the protected data using various techniques.

If the weak function is nonreentrant, when you use the function in concurrent programs, there is an additional race condition risk.

Fix

Avoid functions that use these encryption algorithms. Instead, use a reentrant function that uses a stronger encryption algorithm.

Note

Some implementations of crypt support additional, possibly more secure, encryption algorithms.

Examples

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#define _GNU_SOURCE
#include <pwd.h>
#include <string.h>
#include <crypt.h>

volatile int rd = 1;

const char *salt = NULL;
struct crypt_data input, output;

int verif_pwd(const char *pwd, const char *cipher_pwd, int safe)
{
    int r = 0;
    char *decrypted_pwd = NULL;
    
    switch(safe)
    {
      case 1: 
        decrypted_pwd = crypt_r(pwd, cipher_pwd, &output);
        break;
        
      case 2: 
        decrypted_pwd = crypt_r(pwd, cipher_pwd, &output);
        break;
        
      default:
        decrypted_pwd = crypt(pwd, cipher_pwd); 
        break;
    }
    
    r = (strcmp(cipher_pwd, decrypted_pwd) == 0); 
    
    return r;
}

In this example, crypt_r and crypt decrypt a password. However, crypt is nonreentrant and uses the unsafe Data Encryption Standard algorithm.

Correction — Use crypt_r

One possible correction is to replace crypt with crypt_r.

#define _GNU_SOURCE
#include <pwd.h>
#include <string.h>
#include <crypt.h>

volatile int rd = 1;

const char *salt = NULL;
struct crypt_data input, output;

int verif_pwd(const char *pwd, const char *cipher_pwd, int safe)
{
    int r = 0;
    char *decrypted_pwd = NULL;
    
    switch(safe)
    {
      case 1: 
        decrypted_pwd = crypt_r(pwd, cipher_pwd, &output);
        break;
        
      case 2: 
        decrypted_pwd = crypt_r(pwd, cipher_pwd, &output);
        break;
        
      default:
        decrypted_pwd = crypt_r(pwd, cipher_pwd, &output);  
        break;
    }
    
    r = (strcmp(cipher_pwd, decrypted_pwd) == 0);
    
    return r;
}

Result Information

Group: Security
Language: C | C++
Default: Off
Command-Line Syntax: UNSAFE_STD_CRYPT
Impact: Medium

Version History

Introduced in R2015b

See Also

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