Eric van Gyzen
2016-Aug-22 20:01 UTC
svn commit: r304626 - head/lib/libpam/modules/pam_ssh
I had never looked at pam_ssh before. Does it really ignore authorized_keys and allow authentication using any of the default key file names? After a quick read of the code, that certainly seems to be the case. Does anyone else find that alarming? Sure, it's in my ~/.ssh directory and has appropriate permissions, but that doesn't mean I want to use it for authentication to this machine (or any machine sharing this home directory). That's what authorized_keys is for. I might have created it only to authenticate from this machine to another one. I might have even given it an empty passphrase because that other machine is disposable and I don't really care about it. Eric On 08/22/2016 14:27, Ollivier Robert wrote:> Author: roberto > Date: Mon Aug 22 19:27:20 2016 > New Revision: 304626 > URL: https://svnweb.freebsd.org/changeset/base/304626 > > Log: > Add support for Ed25519 keys. > > Reported by: mwlucas > MFH: 2 weeks > > Modified: > head/lib/libpam/modules/pam_ssh/pam_ssh.8 > head/lib/libpam/modules/pam_ssh/pam_ssh.c > > Modified: head/lib/libpam/modules/pam_ssh/pam_ssh.8 > =============================================================================> --- head/lib/libpam/modules/pam_ssh/pam_ssh.8 Mon Aug 22 19:05:11 2016 (r304625) > +++ head/lib/libpam/modules/pam_ssh/pam_ssh.8 Mon Aug 22 19:27:20 2016 (r304626) > @@ -137,6 +137,8 @@ SSH2 RSA key > SSH2 DSA key > .It Pa $HOME/.ssh/id_ecdsa > SSH2 ECDSA key > +.It Pa $HOME/.ssh/id_ed25519 > +SSH2 Ed25519 key > .El > .Sh SEE ALSO > .Xr ssh-agent 1 , > > Modified: head/lib/libpam/modules/pam_ssh/pam_ssh.c > =============================================================================> --- head/lib/libpam/modules/pam_ssh/pam_ssh.c Mon Aug 22 19:05:11 2016 (r304625) > +++ head/lib/libpam/modules/pam_ssh/pam_ssh.c Mon Aug 22 19:27:20 2016 (r304626) > @@ -81,6 +81,7 @@ static const char *pam_ssh_keyfiles[] = > ".ssh/id_rsa", /* SSH2 RSA key */ > ".ssh/id_dsa", /* SSH2 DSA key */ > ".ssh/id_ecdsa", /* SSH2 ECDSA key */ > + ".ssh/id_ed25519", /* SSH2 Ed25519 key */ > NULL > }; > >
On 8/22/2016 1:01 PM, Eric van Gyzen wrote:> I had never looked at pam_ssh before. Does it really ignore authorized_keys andYeah, that was the entire purpose! https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=15158 For its original purpose I can understand using it, to login *locally*... I am surprised to find this too.> allow authentication using any of the default key file names? After a quick > read of the code, that certainly seems to be the case. Does anyone else find > that alarming? Sure, it's in my ~/.ssh directory and has appropriate > permissions, but that doesn't mean I want to use it for authentication to this > machine (or any machine sharing this home directory). That's what > authorized_keys is for. I might have created it only to authenticate from this > machine to another one. I might have even given it an empty passphrase because > that other machine is disposable and I don't really care about it.At least it is off-by-default:> # grep -r pam_ssh /etc/pam.d|grep auth > /etc/pam.d/system:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/ftp:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/ftpd:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/telnetd:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/xdm:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/imap:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/other:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/sshd:#auth sufficient pam_ssh.so no_warn try_first_pass > /etc/pam.d/pop3:#auth sufficient pam_ssh.so no_warn try_first_passThe implications of uncommenting these are not explained in the files though. The manpage has this gem: "nullok Normally, keys with no passphrase are ignored for authentication purposes. If this option is set, keys with no passphrase will be taken into consideration, allowing the user to log in with a blank password." Why would anyone ever use nullok and use the pam_ssh module? I don't know pam well but I'm sure there's another way to make a check always succeed without a password. So supporting nullok in pam_ssh is just asking for an unknown security bug. I would really like to see nullok support removed from pam_ssh. Why is it even in the remote service files as an example when it is dangerous in those contexts? I find the pam configuration files overly complex and error-prone to begin with, but to discover that there's such a bombshell sitting there is concerning.> > Eric > > On 08/22/2016 14:27, Ollivier Robert wrote: >> Author: roberto >> Date: Mon Aug 22 19:27:20 2016 >> New Revision: 304626 >> URL: https://svnweb.freebsd.org/changeset/base/304626 >> >> Log: >> Add support for Ed25519 keys. >> >> Reported by: mwlucas >> MFH: 2 weeks >> >> Modified: >> head/lib/libpam/modules/pam_ssh/pam_ssh.8 >> head/lib/libpam/modules/pam_ssh/pam_ssh.c >> >> Modified: head/lib/libpam/modules/pam_ssh/pam_ssh.8 >> =============================================================================>> --- head/lib/libpam/modules/pam_ssh/pam_ssh.8 Mon Aug 22 19:05:11 2016 (r304625) >> +++ head/lib/libpam/modules/pam_ssh/pam_ssh.8 Mon Aug 22 19:27:20 2016 (r304626) >> @@ -137,6 +137,8 @@ SSH2 RSA key >> SSH2 DSA key >> .It Pa $HOME/.ssh/id_ecdsa >> SSH2 ECDSA key >> +.It Pa $HOME/.ssh/id_ed25519 >> +SSH2 Ed25519 key >> .El >> .Sh SEE ALSO >> .Xr ssh-agent 1 , >> >> Modified: head/lib/libpam/modules/pam_ssh/pam_ssh.c >> =============================================================================>> --- head/lib/libpam/modules/pam_ssh/pam_ssh.c Mon Aug 22 19:05:11 2016 (r304625) >> +++ head/lib/libpam/modules/pam_ssh/pam_ssh.c Mon Aug 22 19:27:20 2016 (r304626) >> @@ -81,6 +81,7 @@ static const char *pam_ssh_keyfiles[] = >> ".ssh/id_rsa", /* SSH2 RSA key */ >> ".ssh/id_dsa", /* SSH2 DSA key */ >> ".ssh/id_ecdsa", /* SSH2 ECDSA key */ >> + ".ssh/id_ed25519", /* SSH2 Ed25519 key */ >> NULL >> }; >> >>-- Regards, Bryan Drewery -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 473 bytes Desc: OpenPGP digital signature URL: <http://lists.freebsd.org/pipermail/freebsd-security/attachments/20160822/0ef470dd/attachment.sig>