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CWE-759: Use of a One-Way Hash without a Salt
 DescriptionDescription Summary The software uses a one-way cryptographic hash against an input that should not be reversible, such as a password, but the software does not also use a salt as part of the input.
Extended Description This makes it easier for attackers to pre-compute the hash value using dictionary attack techniques such as rainbow tables. It should be noted that, despite common perceptions, the use of a good salt with a hash does not sufficiently increase the effort for an attacker who is targeting an individual password, or who has a large amount of computing resources available, such as with cloud-based services or specialized, inexpensive hardware. Offline password cracking can still be effective if the hash function is not expensive to compute; many cryptographic functions are designed to be efficient and can be vulnerable to attacks using massive computing resources, even if the hash is cryptographically strong. The use of a salt only slightly increases the computing requirements for an attacker compared to other strategies such as adaptive hash functions. See CWE-916 for more details. Common Consequences
Demonstrative ExamplesExample 1 In both of these examples, a user is logged in if their given password matches a stored password: (Bad Code) Example
Language: C unsigned char *check_passwd(char *plaintext) { ctext = simple_digest("sha1",plaintext,strlen(plaintext), ...
);
//Login if hash matches stored hash
if (equal(ctext, secret_password())) {
login_user();
}
} (Bad Code) Example
Language: Java String plainText = new String(plainTextIn); MessageDigest encer = MessageDigest.getInstance("SHA"); encer.update(plainTextIn); byte[] digest = password.digest(); //Login if hash matches stored hash if (equal(digest,secret_password())) { login_user();
} This code does not provide a salt to the hashing function, thus increasing the chances of an attacker being able to reverse the hash and discover the original password. Note this code also exhibits CWE-328 (Reversible One-Way Hash). Example 2 In this example, a new user provides a new username and password to create an account. The program hashes the new user's password then stores it in a database. (Bad Code) Example
Language: Python def storePassword(userName,Password): hasher = hashlib.new('md5')
hasher.update(Password)
hashedPassword = hasher.digest()
# UpdateUserLogin returns True on success, False
otherwise
return updateUserLogin(userName,hashedPassword)
While it is good to avoid storing a cleartext password, the program does not provide a salt to the hashing function, thus increasing the chances of an attacker being able to reverse the hash and discover the original password if the database is compromised. Fixing this is as simple as providing a salt to the hashing function on initialization: (Good Code) Example
Language: Python def storePassword(userName,Password): hasher = hashlib.new('md5',b'SaltGoesHere')
hasher.update(Password)
hashedPassword = hasher.digest()
# UpdateUserLogin returns True on success, False
otherwise
return updateUserLogin(userName,hashedPassword)
Note that regardless of the usage of a salt, the md5 hash is no longer considered secure, so this example still exhibits CWE-327. Observed Examples
Potential Mitigations
Background Details
Relationships
References
Content History
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Page Last Updated:
February 20, 2013
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