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UNIRAS Brief - 98/04 - FreeBSD Security Advisory



 
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   UNIRAS (UK Govt CERT) Briefing Notice - 98/04 dated 01.03.04  Time: 14:50  
  UNIRAS is part of NISCC (National Infrastructure Security Co-ordination Centre)
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  UNIRAS material is also available from its website at www.uniras.gov.uk and
         Information about NISCC is available from www.niscc.gov.uk
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Title
=====

Jailed processes can attach to other jails.

Detail
====== 

The jail(2) system call allows a system administrator to lock up a process and all
its descendants inside a closed environment with very limited ability to affect the
system outside that environment, even for processes with superuser privileges.  
It is an extension of, but far more stringent than, the traditional Unix chroot(2)
system call.



                  ESB-2004.0171 -- FreeBSD-SA-04:03.jail
                Jailed processes can attach to other jails
                               01 March 2004


Product:                jail_attach(2)
Publisher:              FreeBSD
Operating System:       FreeBSD 5.2-RELEASE
                        FreeBSD 5.1-RELEASE
Impact:                 Inappropriate Access
Access Required:        Existing Account
CVE Names:              CAN-2004-0126

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=============================================================================
FreeBSD-SA-04:03.jail                                       Security Advisory
                                                          The FreeBSD Project

Topic:          Jailed processes can attach to other jails

Category:       core
Module:         kernel
Announced:      2004-02-25
Credits:        JAS Group (http://www.cs.mu.oz.au/jas/)
Affects:        FreeBSD 5.1-RELEASE
                FreeBSD 5.2-RELEASE
Corrected:      2004-02-19 23:26:39 UTC (RELENG_5_2, 5.2.1-RC2)
                2004-02-25 20:03:35 UTC (RELENG_5_1, 5.1-RELEASE-p14)
CVE Name:       CAN-2004-0126
FreeBSD only:   YES

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

I.   Background

The jail(2) system call allows a system administrator to lock up a process and all its descendants inside a closed environment with very limited ability to affect the system outside that environment, even for processes with superuser privileges.  It is an extension of, but far more stringent than, the traditional Unix chroot(2) system call.

The jail_attach(2) system call, which was introduced in FreeBSD 5 before 5.1-RELEASE, allows a non-jailed process to permanently move into an existing jail.

II.  Problem Description

A programming error has been found in the jail_attach(2) system call which affects the way that system call verifies the privilege level of the calling process.  Instead of failing immediately if the calling process was already jailed, the jail_attach(2) system call would fail only after changing the calling process's root directory.

III. Impact

A process with superuser privileges inside a jail could change its root directory to that of a different jail, and thus gain full read and write access to files and directories within the target jail.

IV.  Workaround

No workaround is available.

V.   Solution

Do one of the following:

1) Upgrade your vulnerable system to 5.2.1-RELEASE, or to the RELENG_5_2 or RELENG_5_1 security branch dated after the correction date.

OR

2) Patch your present system:

The following patch has been verified to apply to FreeBSD 5.1 and 5.2 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-04:03/jail.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:03/jail.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 system.

VI.  Correction details

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

Branch                                                           Revision
  Path
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RELENG_5_2
  src/sys/kern/kern_jail.c                                       1.34.2.1
RELENG_5_1
  src/UPDATING                                                 1.251.2.16
  src/sys/conf/newvers.sh                                       1.50.2.16
  src/sys/kern/kern_jail.c                                       1.33.2.1
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VII. References

<URL:http://www.cs.mu.oz.au/jas/>
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For additional information or assistance, please contact the HELP Desk by 
telephone or Not Protectively Marked information may be sent via 
EMail to: uniras@xxxxxxxxxxxx

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Tel: +44 (0) 20 7821 1330 and follow the prompts

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UNIRAS wishes to acknowledge the contributions of FreeBSD for the information 
contained in this Briefing. 
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This Briefing contains the information released by the original author. Some 
of the information may have changed since it was released. If the vulnerability 
affects you, it may be prudent to retrieve the advisory from the canonical site 
to ensure that you receive the most current information concerning that problem.

Reference to any specific commercial product, process, or service by trade 
name, trademark manufacturer, or otherwise, does not constitute or imply 
its endorsement, recommendation, or favouring by UNIRAS or NISCC.  The views 
and opinions of authors expressed within this notice shall not be used for 
advertising or product endorsement purposes.

Neither UNIRAS or NISCC shall also accept responsibility for any errors 
or omissions contained within this briefing notice. In particular, they shall 
not be liable for any loss or damage whatsoever, arising from or in connection 
with the usage of information contained within this notice.

UNIRAS is a member of the Forum of Incident Response and Security Teams (FIRST) 
and has contacts with other international Incident Response Teams (IRTs) in 
order to foster cooperation and coordination in incident prevention, to prompt 
rapid reaction to incidents, and to promote information sharing amongst its 
members and the community at large. 
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<End of UNIRAS Briefing>

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