[Bug 1889548] Re: ssh using gssapi will enforce FILE: credentials cache

[Andreas Hasenack]

Toby, you are mostly interested in this because you have some sort of
policy, perhaps one that doesn't allow secrets to be stored on disk in
clear text and protected just by filesystem permissions?

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https://bugs.launchpad.net/bugs/1889548

Title:
  ssh using gssapi will enforce FILE: credentials cache

Status in portable OpenSSH:
  Unknown
Status in openssh package in Ubuntu:
  Confirmed

Bug description:
  Hi,

  ssh connections from a client with the following in ssh_config...

  GSSAPIAuthentication yes
  GSSAPIDelegateCredentials yes

  ... to an ubuntu 20.04 machine result in KRB5CCNAME being set to
  'FILE:/tmp/krb5cc_[uid]_[random]' despite the following in
  /etc/krb5.conf:

  [libdefaults]
   ...
   default_ccache_name = KEYRING:persistent:%{uid}

  This means that we cannot enforce a policy to use KEYRING ccaches
  across our systems.  Authentications which go via the pam stack (e.g.
  login to the machine at the console or over ssh using a password) can
  be configured to use a KEYRING ccache, via libpam-krb5 settings in
  /etc/krb5.conf.

  The FILE: setting seems to be hard-coded in the openssh code (auth-
  krb5.c).  It would be great if ssh(gssapi-with-mic) connections either
  (a) set KRB5CCNAME to the default_ccache_name value, if set in
  /etc/krb5.conf, or (b) didn't set KRB5CCNAME at all, so the system
  default is used.

  Many thanks
  Toby Blake
  School of Informatics
  University of Edinburgh

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