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UNIRAS Brief - 548/04 - FreeBSD-SA-04:15.syscons - Boundary checking errors in syscons



 
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   UNIRAS (UK Govt CERT) Briefing Notice - 548/04 dated 05.10.04  Time: 14:55  
  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
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FreeBSD Security Advisory - FreeBSD-SA-04:15.syscons - Boundary checking errors in syscons
                   

Detail
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The syscons CONS_SCRSHOT ioctl(2) does insufficient validation of its input arguments.  
In particular, negative coordinates or large coordinates may cause unexpected behavior.


                 ESB-2004.0625 -- FreeBSD-SA-04:15.syscons
                    Boundary checking errors in syscons
                              5 October 2004


Product:                syscons (FreeBSD 5.x only)
Publisher:              FreeBSD
Operating System:       FreeBSD
Impact:                 Access Privileged Data
                        Increased Privileges
Access:                 Console/Physical
CVE Names:              CAN-2004-0919
Original Bulletin URL:  ftp://ftp.freebsd.org/pub/FreeBSD/CERT/Advisories/FreeBSD-SA-04:15.syscons.asc

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=============================================================================
FreeBSD-SA-04:15.syscons                                    Security Advisory
                                                          The FreeBSD Project

Topic:          Boundary checking errors in syscons

Category:       core
Module:         sys_dev_syscons
Announced:      2004-10-04
Credits:        Christer Oberg
Affects:        FreeBSD 5.x releases
Corrected:      2004-09-30 17:49:15 UTC (RELENG_5, 5.3-BETA6)
                2004-10-04 17:04:25 UTC (RELENG_5_2, 5.2.1-RELEASE-p11)
CVE Name:       CAN-2004-0919
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

syscons(4) is the default console driver for FreeBSD.  Using the physical keyboard and screen, it provides 
multiple virtual terminals which appear as if they were separate terminals.  One virtual terminal is 
considered current and exclusively occupies the screen and the keyboard; the other virtual terminals are
placed in the background.

II.  Problem Description

The syscons CONS_SCRSHOT ioctl(2) does insufficient validation of its input arguments.  In particular, 
negative coordinates or large coordinates may cause unexpected behavior.

III. Impact

It may be possible to cause the CONS_SCRSHOT ioctl to return portions of kernel memory.  Such memory
might contain sensitive information, such as portions of the file cache or terminal buffers.  This 
information might be directly useful, or it might be leveraged to obtain elevated privileges in some 
way.  For example, a terminal buffer might include a user-entered password.

IV.  Workaround

There is no known workaround.  However, this bug is only exploitable by users who have access to the
physical console or can otherwise open a /dev/ttyv* device node.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to the RELENG_5_2 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 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-04:15/syscons.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:15/syscons.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/UPDATING                                                 1.282.2.19
  src/sys/conf/newvers.sh                                       1.56.2.18
  src/sys/dev/syscons/syscons.c                                 1.409.2.1
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VII. References

<URL:http://cvsweb.freebsd.org/src/sys/dev/syscons/syscons.c.diff?r1=1.428&r2=1.429>
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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 
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<End of UNIRAS Briefing>

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