VBA : Weak hashing algorithm

The used hash function is insecure. Its use can lead to a data confidentiality loss.

Sensitive Data Exposure vulnerabilities take the third place in the “OWASP Top 10 2017” web-application vulnerabilities ranking.

The MD2, MD5, SHA1 hash functions have known vulnerabilities. Finding collisions for MD2 and MD5 functions does not require substantial resources; a similar problem for SHA1 was solved. If these functions are used to store valuable information (such as passwords), its confidentiality can be violated.

The hash function used to store passwords not only should be resistant to collisions but also should not be too fast. This complicates the attack by exhaustive search. For this purpose specialized hash functions have been developed: PBKDF2, bcrypt, scrypt.

Suppose that user passwords are stored on the server in encrypted form with the use of insecure hash function (e.g., MD5). A possible attack scenario:

1. The attacker gains access to the database of encrypted passwords.
2. An attacker exploits a vulnerability of hashing algorithm and calculates the string for which the hash algorithm gives the same value as for the user’s password.
3. The attacker passes the authentication using a calculated string.