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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD ptrace(2) Initialization Error Lets Local Users View Portions of System Memory on the Target System
SecurityTracker Alert ID:  1039809
SecurityTracker URL:
CVE Reference:   CVE-2017-1086   (Links to External Site)
Updated:  Nov 21 2017
Original Entry Date:  Nov 16 2017
Impact:   Disclosure of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 10.3, 10.4, 11.0, 11.1
Description:   A vulnerability was reported in FreeBSD. A local user can obtain potentially sensitive information from system memory.

The ptrace(2) syscall does not properly initialize the ptrace_lwpinfo structure. A local user can run a specially crafted application to obtain potentially sensitive information from kernel memory on the target system.

John Baldwin and Ilja van Sprundel reported this vulnerability.

Impact:   A local user can obtain potentially sensitive information from kernel memory on the target system.
Solution:   FreeBSD has issued a fix.

The FreeBSD 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-17:08.ptrace

Hash: SHA512

FreeBSD-SA-17:08.ptrace                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Kernel data leak via ptrace(PT_LWPINFO)

Category:       core
Module:         ptrace
Announced:      2017-11-15
Credits:        John Baldwin
Affects:        All supported versions of FreeBSD.
Corrected:      2017-11-10 12:28:43 UTC (stable/11, 11.1-STABLE)
                2017-11-15 22:39:41 UTC (releng/11.1, 11.1-RELEASE-p4)
                2017-11-15 22:40:15 UTC (releng/11.0, 11.0-RELEASE-p15)
                2017-11-10 12:31:58 UTC (stable/10, 10.4-STABLE)
                2017-11-15 22:40:32 UTC (releng/10.4, 10.4-RELEASE-p3)
                2017-11-15 22:40:46 UTC (releng/10.3, 10.3-RELEASE-p24)
CVE Name:       CVE-2017-1086

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 ptrace(2) syscall provides the facility for a debugger to control the
execution of the target process and to obtain necessary status information
about it.  The struct ptrace_lwpinfo structure is reported by one of the
ptrace(2) subcommand and contains a lot of the information about the stopped
thread (light-weight process or LWP, thus the name).

II.  Problem Description

Not all information in the struct ptrace_lwpinfo is relevant for the state
of any thread, and the kernel does not fill the irrelevant bytes or short
strings.  Since the structure filled by the kernel is allocated on the
kernel stack and copied to userspace, a leak of information of the kernel
stack of the thread is possible from the debugger.

III. Impact

Some bytes from the kernel stack of the thread using ptrace(PT_LWPINFO)
call can be observed in userspace.

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.

Afterward, reboot the system.

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

Afterward, reboot the system.

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
# fetch
# gpg --verify ptrace.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:> and reboot the

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r325643
releng/10.3/                                                      r325871
releng/10.4/                                                      r325870
stable/11/                                                        r325642
releng/11.0/                                                      r325869
releng/11.1/                                                      r325868
- -------------------------------------------------------------------------

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

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