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FreeBSD ktrace - Users may trace previously privileged processes


FreeBSD-SA-02:30                                            Security Advisory
                                                          The FreeBSD Project

Topic:          Users may trace previously privileged processes

Category:       core
Module:         ktrace
Announced:      2002-07-12
Credits:        Theo DeRaadt <deraadt@OpenBSD.org>
                Darren Reed <darrenr@FreeBSD.org>
Affects:        All releases prior to and including 4.6-RELEASE
                FreeBSD 4.6-STABLE prior to the correction date
Corrected:      2002-07-05 22:36:38 UTC (RELENG_4)
                2002-07-11 16:47:41 UTC (RELENG_4_6)
                2002-07-11 16:47:55 UTC (RELENG_4_5)
                2002-07-11 16:56:05 UTC (RELENG_4_4)
FreeBSD only:   NO

I.   Background

The ktrace utility is a debugging tool that allows users to trace
system calls, I/O, and file system lookup operations executed by or on
behalf of a process and its children.  Since this could potentially
reveal sensitive information, the kernel will normally only allow a
user to trace his or her own processes, and will immediately stop
tracing a process that gains special privileges, for instance by
executing a setuid or setgid binary.  The ktrace utility depends on
the KTRACE kernel option, which is enabled by default.

II.  Problem Description

If a process that had special privileges were to abandon them, it
would become possible for the owner of that process to trace it.
However, that process might still possess and / or communicate
sensitive information that it had obtained before abandoning its
privileges, which would then be revealed to the tracing user.

III. Impact

In theory, local users on systems where ktrace is enabled through
the KTRACE kernel option might obtain sensitive information, such
as password files or authentication keys.  No specific utility is
currently known to be vulnerable to this particular problem.

IV.  Workaround

Recompile the kernel without the KTRACE option, and reboot.

V.   Solution

The following patch has been verified to apply to FreeBSD 4.4, 4.5, and
4.6 systems.

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

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:30/ktrace.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:30/ktrace.patch.asc

b) Apply the patch.

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

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

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Path                                                             Revision
- -------------------------------------------------------------------------
- -------------------------------------------------------------------------

VII. References

Version: GnuPG v1.0.7 (FreeBSD)


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