Alpine Linux Security advisory: OpenSSH-server password authentication bypass
92 points - today at 2:44 PM
Sourcemusl’s crypt() returns the string * as an error indicator when the key is over 256 bytes long. * is also exactly what the stored field contains for every account with no password, so the “hash” matches and the login succeeds.
Does anyone know why musl does this? Are they the only C library that behaves this way?
For a C library that famously tries to adhere to POSIX as much as possible, this seems like a crazy choice. From POSIX standard:
Upon successful completion, crypt() shall return a pointer to the encoded string. The first two bytes of the returned value shall be those of the salt argument. Otherwise, it shall return a null pointer and set errno to indicate the error.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/c...
There's a very detailed trace of how the bug was developed over decades at sshhole.com and the relevant discussion in https://news.ycombinator.com/item?id=50378228
Thanks yeah just woke up, finished making my way through the single-article website and still unclear if other libcs do the same thing (the article says libxcrypt picked it up, but only after musl did it).
worksonmine
today at 4:02 PM
Apparently because some devs didn't check for NULL which resulted in crashes. Weird choice to fix other peoples' bad programming by not conforming to the standard.
TBH that sounds like a straight up bug in that it deviates dangerously from the spec.