*sshole · sshhole.com
sshhole.com
openssh on musl linux has been letting people into password-less accounts since 2016.

are you affected?

  • is your sshd running on musl? (alpine, openwrt, buildroot, yocto)
  • is it not using pam? alpine’s openssh-server doesn’t by default, or maybe you set UsePAM no
  • are password logins still on? they are by default
  • is there an account with just * as its password? key-only users, ldap users, root on alpine
  • and some other account with a real password?
  • then that * account takes any password between 257 and 1024 characters

on alpine’s official aws and azure images that’s the default alpine user, and it has passwordless doas. so it’s root

on debian, ubuntu, fedora or anything else with glibc? going through pam? dropbear? openbsd? you’re fine

  • Daniel Quinn@lemmy.caEnglish
    1·
    10 hours ago

    It’s been years since I was experimenting, trying to set things up properly, but at the time I could swear that I’d have the following set:

    PubkeyAuthentication yes
PasswordAuthentication no
UsePam yes

    and attempts to SSH into the system would still result in a password prompt, even though PasswordAuthentication was set to no. After some experimentation, I found that if I set UsePam to no, you wouldn’t get a password prompt, so that’s what I’ve been doing on every SSH server I’ve had since like, 2000.

    Tinkering with it now though, I see there’s also another directive, KbdInteractiveAuthentication, which when set to no, will ensure I don’t see a password prompt even when UsePam is set to yes. I can only assume that 26ish years ago there was no KbdInteractiveAuthentication, or I just didn’t know about / notice it!

    Well no harm done in my case anyway, as I don’t generally expose SSH servers to the outside world anyway. But it’s good to know that I don’t have to turn off PAM to disable password logins anymore.