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[Launchpad Bug Tracker <2087827@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package pam - 1.5.3-5ubuntu5.4

---------------
pam (1.5.3-5ubuntu5.4) noble-security; urgency=medium

  * SECURITY UPDATE: privilege escalation via pam_namespace
    - debian/patches/pam_namespace_170.patch: sync pam_namespace module to
      version 1.7.0.
    - debian/patches/pam_namespace_post170-*.patch: add post-1.7.0 changes
      from upstream git tree.
    - debian/patches/pam_namespace_revert_abi.patch: revert ABI change to
      prevent unintended issues in running daemons.
    - debian/patches/CVE-2025-6020-1.patch: fix potential privilege
      escalation.
    - debian/patches/CVE-2025-6020-2.patch: add flags to indicate path
      safety.
    - debian/patches/CVE-2025-6020-3.patch: secure_opendir: do not look at
      the group ownership.
    - debian/patches/pam_namespace_o_directory.patch: removed, included in
      patch cluster above.
    - CVE-2025-6020

 -- Marc Deslauriers <marc.deslauriers@xxxxxxxxxx>  Thu, 12 Jun 2025
10:45:28 -0400

** Changed in: pam (Ubuntu Noble)
       Status: Fix Committed => Fix Released

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2025-6020

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https://bugs.launchpad.net/bugs/2087827

Title:
  Pam includes does not look in /usr/lib/pam.d

Status in pam package in Ubuntu:
  Fix Released
Status in pam source package in Noble:
  Fix Released
Status in pam source package in Oracular:
  Fix Committed
Status in pam source package in Plucky:
  Fix Committed
Status in pam source package in Questing:
  Fix Released

Bug description:
  [ Impact ]
  The Debian-specific (and fairly heavily used) @include stanza doesn't load anything from /usr/lib/pam.d, preventing moving default configuration from /etc, which is needed for Ubuntu Core.

  [ Test Plan ]

  In a fresh container:

  # adduser foo
  # mv /etc/pam.d/* /usr/lib/pam.d
  # login 

  You should be able to log in as user foo.

  After exiting the foo session, to check cross-folder inclusion:

  # mv /usr/lib/pam.d/common-password /etc/pam.d
  # mv /usr/lib/pam.d/login /etc/pam.d
  # login

  And finally, to check that they load the /etc file in priority:
  # cp /usr/lib/pam.d/common-account /etc/pam.d
  # echo foobar >> /etc/pam.d/common-account
  # login

  That last one should fail with foobar-related errors in the system
  logs.

  [ Where problems could occur ]

  To minimize user setup breakage potential the test plan ensures that
  there wouldn't be any new shadowing of user config file. Any other
  config that includes something only present in /usr/lib would have
  been broken anyway.

  [Original report]
  We're using libpam in the Ubuntu Core rootfs for the core24 snap (which is pam from Noble). We've run into a sitaution where we would like to move pam.d files into /usr/lib/pam.d instead of /etc/pam.d, and looking at man pages this should be supported. (I.e it always checks /etc/pam.d first, then /usr/lib/pam.d).

  However, there seems to be an issue (or misunderstanding) in terms of
  how `include`'s are loaded. For an installation that has all pam.d
  files in /usr/lib we get this error:

  ```
  [  556.375377] sshd[3553]: PAM _pam_load_conf_file: unable to open config for /etc/pam.d/common-auth
  [  556.377644] sshd[3553]: PAM error loading (null)
  [  556.379731] sshd[3553]: PAM _pam_init_handlers: error reading /usr/lib/pam.d/sshd
  [  556.382681] sshd[3553]: PAM _pam_init_handlers: [Critical error - immediate abort]
  [  556.384512] sshd[3553]: PAM error reading PAM configuration file
  [  556.386397] sshd[3553]: PAM pam_start: failed to initialize handlers
  [  556.389716] sshd[3553]: PAM pam_end: NULL pam handle passed
  [  556.393755] sshd[3553]: fatal: PAM: initialisation failed

  ```

  It seems to correctly read sshd from /usr/lib/pam.d/, however the
  includes it seems it insists on loading through /etc/pam.d. Looking at
  the code:
  https://git.launchpad.net/ubuntu/+source/pam/tree/libpam/pam_handlers.c?h=applied/ubuntu/noble#n227
  it seems that it only checks /etc/pam.d, and not /usr/lib/pam.d. This
  seems to not be in line with the man pages?

  *note* this seem at first glance that there might be a bug in the
  patch `debian/patches/031_pam_include`

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