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FreeBSD-SA-14:27.stdio                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Buffer overflow in stdio

Category:       core
Module:         libc
Announced:      2014-12-10
Credits:        Adrian Chadd and Alfred Perlstein, Norse Corporation
Affects:        FreeBSD 10.1
Corrected:      2014-12-10 08:24:02 UTC (stable/10, 10.1-STABLE)
                2014-12-10 08:35:55 UTC (releng/10.1, 10.1-RELEASE-p1)
CVE Name:       CVE-2014-8611

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

I.   Background

The standard I/O library provides a simple and efficient buffered stream
I/O interface.  The library writes buffered data when it is full or when
the application explicitly request so by calling the fflush(3) function.

II.  Problem Description

A programming error in the standard I/O library's __sflush() function could
erroneously adjust the buffered stream's internal state even when no write
actually occurred in the case when write(2) system call returns an error.

III. Impact

The accounting mismatch would accumulate, if the caller does not check for
stream status and will eventually lead to a heap buffer overflow.

Such overflows may lead to data corruption or the execution of arbitrary
code at the privilege level of the calling program.

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.

# fetch http://security.FreeBSD.org/patches/SA-14:27/stdio.patch
# fetch http://security.FreeBSD.org/patches/SA-14:27/stdio.patch.asc
# gpg --verify stdio.patch.asc

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

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

c) Recompile the operating system using buildworld and installworld as
described in <URL:http://www.FreeBSD.org/handbook/makeworld.html>.

Reboot the system.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r275667
releng/10.1/                                                      r275670
- -------------------------------------------------------------------------

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:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-8611>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:27.stdio.asc>
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