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Subject: Unixware SCOhelp http server format string vulnerability
From: Iván (core.lists.bugtraqCORE-SDI.COM)
Date: Wed Sep 27 2000 - 15:40:50 CDT


                                               CORE SDI Inc.
                                       http://www.core-sdi.com

              Unixware SCOhelp http server format string vulnerability

Date Published: 09/27/00

Advisory ID: CORE-092700

Bugtraq ID: 1717

CVE CAN: None currently assigned.

Title: Unixware SCOhelp http server format string vulnerability

Class: Input validation error

Remotely Exploitable: Yes

Locally Exploitable: Yes

Vulnerability Description:

 SCO Unixware 7 default installation includes scohelp, an http
 server that listens on port 457/tcp and allows access to manual
 pages and other documentation files. The search CGI script provided
 for that purpose has a vulnerability that could allow any remote
 attacker to execute arbitrary code on the vulnerable machine with
 privileges of user "nobody".
 This poses a threat that could result in the remote compromise of
 the vulnerable host and provide a staging point from where an attacker
 could escalate privileges.

Vulnerable Packages/Systems:
 Unixware 7

Solution/Vendor Information/Workaround:

 Contact the vendor for a fix

 In the meantime, disabling the http server on port 457/tcp
 will prevent exploitation of the vulnerability. However, this
 will also make access to the documentation unavailable.

 The following is a workaround supplied by the vendor:
 To apply the workaround to your system you must:

 1) Log into the system as root

 2) cd /usr/ns-home/httpd-scohelphttp/search97

 3) mkdir ./securebin

 4) mv ./bin/vtopic ./securebin

 5) Using your favourite editor create a new version of vtopic
    in the /usr/ns-home/httpd-scohelphttp/search97/bin
    directory containing the following:
--------------------------------------------------------------------
#!/bin/sh
VERITYBIN=/usr/ns-home/httpd-scohelphttp/search97/bin
SECUREBIN=/usr/ns-home/httpd-scohelphttp/search97/securebin
configPath=$VERITYBIN/inetsrch.ini
export configPath

# If POST method, convert to QUERY_STRING
if [ -z "$QUERY_STRING" ]
then
        POST=1
        eval `$VERITYBIN/cgiparse -init`
else
        POST=0
fi

# Exit if not set
if [ -z "$QUERY_STRING" ]
then
        exit 1
fi

# Now strip out insecure character %25
QUERY_STRING=`echo "$QUERY_STRING" | sed "s/%25/+/g"`

# First check for multiple ViewTemplate fields
# which could fool vtopic
COUNT=`$VERITYBIN/cgiparse -count -value ViewTemplate 2> /dev/null`
if [ "$COUNT" -gt 1 ]
then
        exit 1
fi

# First check for multiple ResultTemplate fields
# which could fool vtopic
COUNT=`$VERITYBIN/cgiparse -count -value ResultTemplate 2> /dev/null`
if [ "$COUNT" -gt 1 ]
then
        exit 1
fi

# Now check for correct path in ViewTemplate if it has one
if echo "$QUERY_STRING" | egrep -i '&ViewTemplate=' > /dev/null 2>&1
then
        MATCH=`cgiparse -value ViewTemplate 2> /dev/null | egrep -i
'[-A-Za-z0-9_.]+/_SearchTemplates/docview.hts'`
        if [ -z "$MATCH" ]
        then
                exit 1
        fi
fi

# Now check for correct path in ResultTemplate if it has one
if echo "$QUERY_STRING" | egrep -i '&ResultTemplate=' > /dev/null 2>&1
then
        MATCH=`cgiparse -value ResultTemplate 2> /dev/null | egrep -i
'[-A-Za-z0-9_.]+/_SearchTemplates/result.hts'`
        if [ -z "$MATCH" ]
        then
                exit 1
        fi
fi

# OK, so proceed
if [ "$POST" -eq 1 ]
then
        export CONTENT_LENGTH
        echo "$QUERY_STRING" | $SECUREBIN/vtopic
else
        export QUERY_STRING
        $SECUREBIN/vtopic
fi
--------------------------------------------------------------------

6) chmod +x vtopic

This script acts as a wrapper to the vtopic binary and blocks
queries that can:

  1) Allow a remote user to request to view a world readable file
     like /etc/passwd

  2) Cause a failure like the one described in your email to SCO.

Vendor notified on: September 11th, 2000

Credits:

 This vulnerability was discovered by Juliano Rizzo of CORE SDI Inc.,
 Buenos Aires, Argentina.

 This advisory was drafted with the help of the SecurityFocus.com
 Vulnerability Help Team. For more information or assistance drafting
 advisories please mail vulnhelpsecurityfocus.com.

 Fix information and the workaround was provided by the SCO Security Group
 It can be contacted at security-alertsco.com

Technical Description - Exploit/Concept Code:

 There is a user supplied format string bug in the vtopic CGI script that
 could be abused to execute arbitrary code. By sending a request with the
 following URI:

  http://target:457/search97cgi/vtopic?Action=\
  FilterSearch&filter=&queryText=%25x

 The server will elicit the following response:

--
Internal error: STR_sprintf: Invalid format (Error E1-0142 (Query
Builder): Invalid character '%' (0x25))

Result Search failed: -40

Result Error E1-0142 (Query Builder): Invalid character '

Result Error E1-0130 (Query Builder): Syntax error in query string near character 1

Result Error E1-0133 (Query Builder): Error parsing query: 81888e0

Result VdkSearchNew failed, error -40

Result Request failed for REQUEST_METHOD=, QUERY_STRING=

Component Component (vsearch) failed in processing request, -2

Action Action (FilterSearch) failed while processing request in component (vsearch), -2

Service Manager Action (FilterSearch) failed in processing request, -2 S97IS Service manager failed to process request --

Note the line: Error E1-0133 (Query Builder): Error parsing query: 81888e0

This shows that the server is interpreting the %x argument passed in the URI as the "queryText" value. Supplying a carefully built value for the queryText argument an attacker can change the program flow and execute arbitrary code.

DISCLAIMER:

The contents of this advisory are copyright (c) 2000 CORE SDI Inc. and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.

$Id: SCOhelphttp-advisory.txt,v 1.6 2000/09/27 20:36:34 iarce Exp $ -- "Understanding. A cerebral secretion that enables one having it to know a house from a horse by the roof on the house, It's nature and laws have been exhaustively expounded by Locke, who rode a house, and Kant, who lived in a horse." - Ambrose Bierce

==================[ CORE Seguridad de la Informacion S.A. ]========= Iván Arce Presidente PGP Fingerprint: C7A8 ED85 8D7B 9ADC 6836 B25D 207B E78E 2AD1 F65A email : iarcecore-sdi.com http://www.core-sdi.com Pte. Juan D. Peron 315 Piso 4 UF 17 1038 Capital Federal Buenos Aires, Argentina. Tel/Fax : +(54-11) 4331-5402 Casilla de Correos 877 (1000) Correo Central =====================================================================

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