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FreeBSD-SA-14:25.setlogin                                   Security Advisory
                                                          The FreeBSD Project

Topic:          Kernel stack disclosure in setlogin(2) / getlogin(2)

Category:       core
Module:         kernel
Announced:      2014-11-04
Credits:        Mateusz Guzik
Affects:        All supported versions of FreeBSD.
Corrected:      2014-11-04 23:29:57 UTC (stable/10, 10.1-PRERELEASE)
                2014-11-04 23:34:46 UTC (releng/10.1, 10.1-RC4-p1)
                2014-11-04 23:34:46 UTC (releng/10.1, 10.1-RC3-p1)
                2014-11-04 23:34:46 UTC (releng/10.1, 10.1-RC2-p3)
                2014-11-04 23:31:17 UTC (releng/10.0, 10.0-RELEASE-p12)
                2014-11-04 23:30:47 UTC (stable/9, 9.3-STABLE)
                2014-11-04 23:33:46 UTC (releng/9.3, 9.3-RELEASE-p5)
                2014-11-04 23:33:17 UTC (releng/9.2, 9.2-RELEASE-p15)
                2014-11-04 23:32:45 UTC (releng/9.1, 9.1-RELEASE-p22)
                2014-11-04 23:30:23 UTC (stable/8, 8.4-STABLE)
                2014-11-04 23:32:15 UTC (releng/8.4, 8.4-RELEASE-p19)
CVE Name:       CVE-2014-8476

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The setlogin(2) system call sets the login name of the user associated
with the current session.  The getlogin(2) routine returns the login name
of the user associated with the current session, as previously set by
setlogin(2).

II.  Problem Description

When setlogin(2) is called while setting up a new login session, the
login name is copied into an uninitialized stack buffer, which is then
copied into a buffer of the same size in the session structure.  The
getlogin(2) system call returns the entire buffer rather than just the
portion occupied by the login name associated with the session.

III. Impact

An unprivileged user can access this memory by calling getlogin(2) and
reading beyond the terminating NUL character of the resulting string.
Up to 16 (FreeBSD 8) or 32 (FreeBSD 9 and 10) bytes of kernel memory
may be leaked in this manner for each invocation of setlogin(2).

This memory may contain sensitive information, such as portions of the
file cache or terminal buffers, which an attacker might leverage to
obtain elevated privileges.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 9.1]
# fetch https://security.FreeBSD.org/patches/SA-14:25/setlogin-91.patch
# fetch https://security.FreeBSD.org/patches/SA-14:25/setlogin-91.patch.asc
# gpg --verify setlogin-91.patch.asc

[All other versions]
# fetch https://security.FreeBSD.org/patches/SA-14:25/setlogin.patch
# fetch https://security.FreeBSD.org/patches/SA-14:25/setlogin.patch.asc
# gpg --verify setlogin.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/8/                                                         r274108
releng/8.4/                                                       r274111
stable/9/                                                         r274109
releng/9.1/                                                       r274112
releng/9.2/                                                       r274113
releng/9.3/                                                       r274114
stable/10/                                                        r274107
releng/10.0/                                                      r274110
releng/10.1/                                                      r274115
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-8476>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-14:25.setlogin.asc>
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