Use of Predictable Algorithm in Random Number Generator in beestat/app
Reported on
Jun 26th 2021
✍️ Description
The random number generator implemented by mt_rand() on session keys is not suitable for cryptographic purposes (generation of tokens, passwords, or cryptographic keys) either. mt_rand function that produces predictable values is utilized as a source of randomness in a security-sensitive environment, insecure randomness mistakes arise.
In this case, function generate_session_key() generated weak random numbers is mt_rand in /api/cora/session.php at line 252.
🕵️♂️ Proof of Concept
// POC.php
https://github.com/ambionics/mt_rand-reverse/blob/master/display_mt_rand.php
💥 Impact
This vulnerability is capable of letting the attacker guess the session key of any user.
Hey x3rz, since I was not able to find a security policy or other method of contact, I've created an issue on the repo asking a way to responsibly disclose this vulnerability. Waiting to hear back; good job!
I have marked this as a valid weakness, although I disagree with the severity. Hashing the value after generation means it cannot be reverse-engineered. The uniqid() function has microsecond precision, and adding mt_rand() on top of that adds even more randomness to the generated key. That on top of the application rate limiting makes this a virtual non-issue.
That said, I have no issues updating this to use a cryptographically-secure algorithm like openssl_random_pseudo_bytes() or random_bytes().