Uninitialized struct field in the fix for CVE-2015-5600 causes random auth failures

[Benn Sundsrud]

In Ubuntu 12.04, the fix for CVE-2015-5600[1] just hit upstream in package openssh-server_5.9p1-5ubuntu1.6, breaking authentication mechanisms that rely on the keyboard-interactive method. This patch introduces the field 'devices_done' to the KbdintAuthctxt struct, but does not initialize the field in the kbdint_alloc() function. On Linux, this ends up filling that field with junk data. The attached patch against adds the initialization of the `devices_done` field alongside the existing initialization code. This has also been reported upstream.

Reproducing:

Install openssh-server_5.9p1-5ubuntu1.6
Add an authentication mechanism that uses the keyboard-interactive method (like libpam-google-authenticator)
Attempt to log in via the above mechanism. Instead of consistently prompting the user for input, it will sometimes fall straight through to password auth because the devices_done bit field is initialized with garbage data.

Downgrading to openssh-server_5.9p1-5ubuntu1.4 solves the issue.

[1]: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/auth2-chall.c.diff?r1=1.42&r2=1.43&f=h

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "CVE-2015-5600_initialize_struct.patch" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Marc Deslauriers (mdeslaur)]

I have uploaded updated packages to fix this issue to the following PPA:

https://launchpad.net/~ubuntu-security-proposed/+archive/ubuntu/ppa/+packages

Please test and see if they fix the issue in your environment. If they do, and they pass QA, I will publish them as security updates tomorrow.

Thanks.

[Launchpad Janitor (janitor)]

This bug was fixed in the package openssh - 1:6.7p1-6ubuntu2

---------------
openssh (1:6.7p1-6ubuntu2) wily; urgency=medium

  * SECURITY REGRESSION: random auth failures because of uninitialized
    struct field (LP: #1485719)
    - debian/patches/CVE-2015-5600-2.patch: properly initialize field in
      auth2-chall.c.

 -- Marc Deslauriers <email address hidden> Mon, 17 Aug 2015 22:13:25 -0400

[Benn Sundsrud (benn-sundsrud)]

That package works on my test box. Thanks Marc!

[Launchpad Janitor (janitor)]

This bug was fixed in the package openssh - 1:5.9p1-5ubuntu1.7

---------------
openssh (1:5.9p1-5ubuntu1.7) precise-security; urgency=medium

  * SECURITY REGRESSION: random auth failures because of uninitialized
    struct field (LP: #1485719)
    - debian/patches/CVE-2015-5600-2.patch:

 -- Marc Deslauriers <email address hidden> Mon, 17 Aug 2015 21:53:19 -0400

[Launchpad Janitor (janitor)]

This bug was fixed in the package openssh - 1:6.6p1-2ubuntu2.3

---------------
openssh (1:6.6p1-2ubuntu2.3) trusty-security; urgency=medium

  * SECURITY REGRESSION: random auth failures because of uninitialized
    struct field (LP: #1485719)
    - debian/patches/CVE-2015-5600-2.patch:

 -- Marc Deslauriers <email address hidden> Mon, 17 Aug 2015 21:52:52 -0400

[Launchpad Janitor (janitor)]

This bug was fixed in the package openssh - 1:6.7p1-5ubuntu1.3

---------------
openssh (1:6.7p1-5ubuntu1.3) vivid-security; urgency=medium

  * SECURITY REGRESSION: random auth failures because of uninitialized
    struct field (LP: #1485719)
    - debian/patches/CVE-2015-5600-2.patch:

 -- Marc Deslauriers <email address hidden> Mon, 17 Aug 2015 21:49:49 -0400

[Colin Watson (cjwatson)]

This patch is unnecessary with OpenSSH 6.5p1 and newer, because kbdint_alloc now uses xcalloc rather than xmalloc and thus zeroes the entire structure. The regression fix was thus only needed for precise and not for later releases; I'll drop it from wily shortly when resyncing with unstable, in the cause of keeping a smaller delta against upstream.