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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD Kernel sendfile(2) Discloses Kernel Memory Contents to Local Users
SecurityTracker Alert ID:  1029013
SecurityTracker URL:
CVE Reference:   CVE-2013-5666   (Links to External Site)
Date:  Sep 10 2013
Impact:   Disclosure of system information, Disclosure of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 9.2-RC1, 9.2-RC2
Description:   A vulnerability was reported in the FreeBSD Kernel. A local user can obtain kernel memory contents.

A local user can invoke sendfile(2) with a length value that is greater than the length of the file being transmitted to cause the system to pad the packet with contents from kernel memory.

Ed Maste reported this vulnerability.

Impact:   A local user can obtain kernel memory contents.
Solution:   The vendor has issued a fix.

The vendor's advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Access control error

Message History:   None.

 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-13:11.sendfile

Hash: SHA1

FreeBSD-SA-13:11.sendfile                                   Security Advisory
                                                          The FreeBSD Project

Topic:          Kernel memory disclosure in sendfile(2)

Category:       core
Module:         sendfile
Announced:      2013-09-10
Credits:        Ed Maste
Affects:        FreeBSD 9.2-RC1 and 9.2-RC2
Corrected:      2013-09-10 10:07:21 UTC (stable/9, 9.2-STABLE)
                2013-09-10 10:08:20 UTC (releng/9.2, 9.2-RC1-p2)
                2013-09-10 10:08:20 UTC (releng/9.2, 9.2-RC2-p2)
CVE Name:       CVE-2013-5666

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

I.   Background

The sendfile(2) system call allows a server application (such as an
HTTP or FTP server) to transmit the contents of a file over a network
connection without first copying it to application memory.  High
performance servers such as Apache and ftpd use sendfile.

II.  Problem Description

On affected systems, if the length passed to sendfile(2) is non-zero
and greater than the length of the file being transmitted, sendfile(2)
will pad the transmission up to the requested length or the next
pagesize boundary, whichever is smaller.

The content of the additional bytes transmitted in this manner depends
on the underlying filesystem, but may potentially include information
useful to an attacker.

III. Impact

An unprivileged user with the ability to run arbitrary code may be
able to obtain arbitrary kernel memory contents.

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 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 9.2-STABLE]
# fetch
# fetch
# gpg --verify sendfile-9.2-stable.patch.asc

[FreeBSD 9.2-RC1 and 9.2-RC2]
# fetch
# fetch
# gpg --verify sendfile-9.2-rc.patch.asc

b) Apply the patch.

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

c) Recompile your kernel as described in
<URL:> and reboot the

3) 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

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r255443
releng/9.2/                                                       r255444
- -------------------------------------------------------------------------

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://

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


VII. References


The latest revision of this advisory is available at
Version: GnuPG v1.4.14 (FreeBSD)


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