Security News > 2023 > January > Serious Security: The Samba logon bug caused by outdated crypto

Astonishingly, the CVE-2022-38023 vulnerability existed in the first place because both Windows and Samba still supported a style of integrity protection based on the long-deprecated hashing algorithm MD5. Simply put, network authentication using Microsoft's version of the Kerberos protocol still allowed data to be integrity-protected using flawed cryptography.

Assuming a reliable algorithm, with no exploitable weaknesses, you'd expect that a hash with X bits of output would need about 2X-1 tries to find a second input that collided with the hash of an existing file.

If there are 2X different possible hash outputs, you'd hope to hit a 50:50 chance of finding an input with a specific, pre-determined hash after about half as many tries, and 2X/2 = 2X-1.

You can't easily go backwards from an MD5 hash to uncover anything about the specific input that produced it, which is another cryptographic promise that a reliable hash needs to keep.

Once the first hash is calculated, the key has a different set of bits flipped, gets prepended to that first hash value, and this new input data is hashed a second time.

Instead, the heart of the bug is line 11, where the data you're trying to hash so it can be authenticated is compressed into a fixed-length string.

News URL

https://nakedsecurity.sophos.com/2023/01/30/serious-security-the-samba-logon-bug-caused-by-outdated-crypto/