One of my website was hacked, during the cleanup process I found a few files with some cryptic code. Doing a bit of research I found that a piece of string was getting executed without being passed to a function. I am a bit stumped as to how PHP is executing that string? Does PHP automatically eval strings?
Here's a piece of the string I found $VCAzeJzvMaKiJXvfeJZd='99V38=jVN4C;.Z<'^'ZK3RLX50;Z OG5R'; when I add it to a test script as below it produces create_function:
<?php
echo $VCAzeJzvMaKiJXvfeJZd='99V38=jVN4C;.Z<'^'ZK3RLX50;Z OG5R';
// output : create_function
P.S: in the malicious file I found, there's no echo, just a long cryptic string. I added echo in the code above for test purpose.
No, strings don't automagically get eval'ed, in this case it's actually 2 strings being bitwise Xor'd. Note the ^ between the 2 strings.
Related
I am having JSON strings that sometimes get cut off in my database. Unsurprisingly, they cannot be parsed by the PHP function json_decode(). Instead of returning null, I want the function to return the value that are still readable. For this, I need to add "]} chars and possibly even : in order to produce valid JSON again.
E.g.
{"a":"b","c":"d
should become
{"a":"b","c":"d"}
This sounds complex. Are there any solution to this except writing a full-blown JSON parser?
Are there libraries or functions for that?
PHP doesn't have any built-in functions to do this.
I've searched for "PHP fix broken JSON automatically" and found an opensource library which tries to accomplish this task.
Please take a look: https://github.com/adhocore/php-json-fixer
I am keeping record of every request made to my website. I am very aware of the security measurements that need to be taken before executing any MySQL query that contains data coming from query strings. I clean it as much as possible from injections and so far all tests have been successful using:
htmlspecialchars, strip_tags, mysqli_real_escape_string.
But on the logs of pages visited I find query strings of failed hack attempts that contain a lot of php code:
?1=%40ini_set%28"display_errors"%2C"0"%29%3B%40set_time_limit%280%29%3B%40set_magic_quotes_runtime%280%29%3Becho%20%27->%7C%27%3Bfile_put_contents%28%24_SERVER%5B%27DOCUMENT_ROOT%27%5D.%27/webconfig.txt.php%27%2Cbase64_decode%28%27PD9waHAgZXZhb
In the previous example we can see:
display_errors, set_time_limit, set_magic_quotes_runtime, file_put_contents
Another example:
/?s=/index/%5Cthink%5Capp/invokefunction&function=call_user_func_array&vars[0]=file_put_contents&vars[1][]=ctlpy.php&vars[1][]=<?php #assert($_REQUEST["ysy"]);?>ysydjsjxbei37$
This one is worst, there is even some <?php and $_REQUEST["ysy"] stuff in there. Although I am able to sanitize it, strip tags and encode < or > when I decode the string I can see the type of requests that are being sent.
Is there any way to detect a string that contains php code like:
filter_var($var, FILTER_SANITIZE_PHP);
FYI: This is not a real function, I am trying to give an idea of what I am looking for.
or some sort of function:
function findCode($var){
return ($var contains PHP) ? true : false
}
Again, not real
No need to sanitize, that has been taken care of, just to detect PHP code in a string. I need this because I want to detect them and save them in other logs.
NOTE: NEVER EXECUTE OR EVAL CODE COMING FROM QUERY STRINGS
After reading lots of comments #KIKO Software came up with an ingenious idea by using PHP tokenizer, but it ended up being extremely difficult because the string that is to be analyzed needed to have almost prefect syntax or it would fail.
So the best solution that I came up with is a simple function that tries to find commonly used PHP statements, In my case, especially on query strings with code injection. Another advantage of this solution is that we can modify and add to the list as many PHP statements as we want. Keep in mind that making the list bigger will considerably slow down your script. this functions uses strpos instead of preg_match (regex ) as its proven to perform faster.
This will not find 100% PHP code inside a string, but you can customize it to find as much as is required, never include terms that could be used in regular English, like 'echo' or 'if'
function findInStr($string, $findarray){
$found=false;
for($i=0;$i<sizeof($findarray);$i++){
$res=strpos($string,$findarray[$i]);
if($res !== false){
$found=true;
break;
}
}
return $found;
}
Simply use:
$search_line=array(
'file_put_contents',
'<?=',
'<?php',
'?>',
'eval(',
'$_REQUEST',
'$_POST',
'$_GET',
'$_SESSION',
'$_SERVER',
'exec(',
'shell_exec(',
'invokefunction',
'call_user_func_array',
'display_errors',
'ini_set',
'set_time_limit',
'set_magic_quotes_runtime',
'DOCUMENT_ROOT',
'include(',
'include_once(',
'require(',
'require_once(',
'base64_decode',
'file_get_contents',
'sizeof',
'array('
);
if(findInStr("this has some <?php echo 'PHP CODE' ?>",$search_line)){
echo "PHP found";
}
I have following code:
<?php
$param = $_GET['param'];
echo $param;
?>
when I use it like:
mysite.com/test.php?param=2+2
or
mysite.com/test.php?param="2+2"
it prints
2 2
not
4
I tried also eval - neither worked
+ is encoded as a space in query strings. To have an actual addition sign in your string, you should use %2B.
However, it should be noted this will not perform the actual addition. I do not believe it is possible to perform actual addition inside the query string.
Now. I would like to stress to avoid using eval as if it's your answer, you're asking the wrong question. It's a very dangerous piece of work. It can create more problems than it's worth, as per the manual specifications on this function:
The eval() language construct is very dangerous because it allows
execution of arbitrary PHP code. Its use thus is discouraged. If you
have carefully verified that there is no other option than to use this
construct, pay special attention not to pass any user provided data
into it without properly validating it beforehand.
So, everything that you wish to pass into eval should be screened against a very.. Very strict criteria, stripping out other function calls and other possible malicious calls & ensure that 100% that what you are passing into eval is exactly as you need it. No more, no less.
A very basic scenario for your problem would be:
if (!isset($_GET['Param'])){
$Append = urlencode("2+2");
header("Location: index.php?Param=".$Append);
}
$Code_To_Eval = '$Result = '.$_GET['Param'].';';
eval($Code_To_Eval);
echo $Result;
The first lines 1 through to 4 are only showing how to correctly pass a character such a plus symbol, the other lines of code are working with the data string. & as #andreiP stated:
Unless I'm not mistaking the "+" is used for URL encoding, so it would
be translated to a %, which further translates to a white space.
That's why you're getting 2 2
This is correct. It explains why you are getting your current output & please note using:
echo urldecode($_GET['Param']);
after encoding it will bring you back to your original output to which you want to avoid.
I would highly suggest looking into an alternative before using what i've posted
I have a php script that handles a form input. For design reasons both a bit out of my control, and which I do not entirely wish to change, I have to call a perl script with the parameters specified in the html form.
I sanitized all inputs and then output them to a file called input, which is read by the perl script named, for sake of brevity in this question, script.pl. Script.pl should do some stuff and then write all outputs to a file named output.
I call the perl script from php like so:
system('perl script.pl 2>errors');
No good, nothing happens. output is not created, errors is not created, and the side effect does not occur.
My apache runs as www-data user and group id. My directory is set with 775 settings with ownership as me:www-data. (My user name is replaced with "me" for sakes for privacy).
My question is two fold:
1) Am I doing this wrong? If so how should I improve upon the code?
2) Is there a more sane way to catch errors in system execution?
After programming in perl for a while, php feels like a pain in the ass.
OS: Ubuntu server edition
popen can be used to get the shell's response. that is your best bet. Which can help you debug why system is angry. also, if your pl is saying "hello" and "bye", popen can even read that.
If the command to be executed could not be found, a valid resource is returned. This may seem odd, but makes sense; it allows you to access any error message returned by the shell
Ideally, I would have taken data from stdin and written to stdout. popen would allow neat access to both.
popen('pwd;perl script.pl 2>errors;echo done');
then you can see where were you (directory) when system got called and did it "done".
In the past I have used shell_exec() or backticks to accomplish this.
The documentation for shell_exec's return value indicates it is identical to the backtick operator:
Return Values
The output from the executed command.
Hope that helps.
system() only returns the status code.
$var = shell_exec ("ls");
print $var;
$var = `ls -l`;
print $var;
Is perl in the path? Maybe you need to specify it fully (e.g. /usr/bin/perl). Is system() returning false, indicating a failure? If you try something simpler, like system('/usr/bin/true', $retval), does $retval get set to 1?
Take a look at the PHP system() documentation. The following is the function prototype of system():
string system ( string $command [, int &$return_var ] )
Pass in a 2nd argument and then print out the return string as well as the second variable. See what the error says.
This is the preg_match i am trying to use to find specific text in text file.
if (preg_match($regexp,$textFile,$result) > 0) {
echo "Found ".$result[0];
} else {
echo "Not found";
}
However, the result is always Found and nothing more. The result array is empty. Now i read that preg_match can't work with long strings.
My text file is about 300KB so thats 300000 characters i guess.
I am 100% sure that the searched string is in the text file, and the fact that preg_match function returns value above 0 means it found it, but it didn't place it into the result array somehow.
So my question would be, how do i make it work?
regexp would be /[specific text]\{(\d*)\}/ so, of course i want to be able to get the number in the parentheses.
You'll be glad I found this question. As of PHP 5.2, they introduced a limit on the size of text that the PCRE functions can be used on, which defaults to 100k. That's not so bad. The bad part is that it silently fails if greater than that.
The solution? Up the limit. The initialization parameter is pcre.backtrack_limit.
No, don't up the pcre limit. Don't do things without understand them. This is a common bug with php pcre
Read this awesome answer by #ridgerunner :
https://stackoverflow.com/a/7627962/1077650
this class of regex will repeatably (and silently) crash Apache/PHP with an unhandled segmentation fault due to a stack overflow!
PHP Bug 1: PHP sets: pcre.recursion_limit too large.
PHP Bug 2: preg_match() does not return FALSE on error.