Exec($_GET

https://github.com/search?q=exec%28%24_GET&ref=cmdform&type=Code

by throwaway2048 • 12 years ago

212 122 12 years ago

github.com

distracteddev90• 12 years ago

I don't get this?

Cymen• 12 years ago

It is showing example of the PHP exec call running based on a GET parameter from a request. A really big security hole.

http://www.php.net/manual/en/function.exec.php

http://www.php.net/manual/en/reserved.variables.get.php

jamestanderson• 12 years ago

This shows, in a very public way, a bunch of instances where code explicitly allows for arbitrary code execution (a security no-no.)

BHSPitMonkey• 12 years ago

It's a large quantity of instances of PHP code that executes arbitrary user input (URL parameters) on the server.

patopop007• 12 years ago

Its mean to show all the projects on Github that are vulnerable to injection attacks. An attack can maliciously create a GET request that escapes out the current command and then execute arbitrary commands.

adamnemecek2• 12 years ago

It's a really dumb RCE exploit. Like maybe the dumbest there can be.

revscat• 12 years ago

It is executing shell commands based on what you pass in through a request parameter. Since there is no filtering going on, you could, I suppose, pass in an entire bash script and have a good ol' time.

mikeytown2• 12 years ago

I found a legit repo for this code https://github.com/andresriancho/w3af-moth "A set of vulnerable PHP scripts used to test w3af's vulnerability detection features."

elwell2• 12 years ago

Which points out that the context has to considered as well. E.g., if it's a personal intranet or password protected page, this may not be vulnerability.

utunga• 12 years ago

Yes. No.

xai• 12 years ago

What if a hacker would have access to a user of said personal intranet, or would find a way to bypass the password protected page. Then he'd be able to execute anything on the server, even stuff the user he hacked shouldn't be able to access. So no, this is always a vulnerability.

robbles• 12 years ago

It would still be vulnerable to a CSRF attack. The attacker can just get a logged-in user to launch their exploit, through a vulnerable site they frequent or even a link or image in an email.

kingnight• 12 years ago

Something like this might make a great feature for github — exploit code review warnings/alerts.

ghayes• 12 years ago

It would actually be a nice to build an optional warning feature into `git` itself. You could download some known common issues and the script would generate warnings if you checked in corresponding code. E.g.

    git add id_rsa
    
    WARNING: You may have just staged a private key.

or better

    echo '{"password": "mypassword"}' > config.json
    git add config.json

    WARNING: You may have just staged a password.

lloeki• 12 years ago

Write git hooks and share them as "git-lint"

bananas2• 12 years ago

Proving once and for all that if you give someone a hand grenade, they'll go marching around with the pin out on the street.

catmanjan• 12 years ago

"We've found 99,841 code results"

Someone should write a script that automatically raises an issues for each line and each project, it's probably possible, but I'm chronically lazy.

rplnt• 12 years ago

As noted in other comment(s), there are legit uses for this.

ircmaxell2• 12 years ago

Can you please provide just one? No other comment does that.

And to be clear, I'm talking about providing at least one legit use for passing user input directly to exec without any kind of filtering...

munimkazia• 12 years ago

Well, some of them are false positives.

monksy• 12 years ago

I thought about doing the exact same thing. But I wonder about the: limiting of the issue creation API on github and false positives. [The variable has been sanitized prior to being executed]

JelteF• 12 years ago

I remember reading about something like this and Github their response was that the guy should stop according to their ToS. Their ToS blocks stuff like this to prevent spamming.

tlrobinson2• 12 years ago

I don't like Issue bots, but it could actually be a huge value-add for GitHub to integrate these kinds of checks (as well as hardcoded credentials, etc) for their users.

marlin4• 12 years ago

After looking at the search result i can see that most of the results have legit reasons.

Instead of half-assing the problem, please dedicate 10 minute of your life to look in, analyze & report one or two of the problems you find.

Also explain why you think this is an security issue.

You will:

  * help someone out by pointing out an issue

  * hopefully educate the person how to write better code

  * educate yourself in reading and understanding others spaghetti code

deckiedan2• 12 years ago

As a theoretical aside, I wonder if it'd be possible to have a typesystem based solution to these kinds of problems - where variables coming from the user (or from another program) are considered 'unsafe' and the compiler refuses to let exec() or whatever use them until they've been through a cleaner/tester of some kind... (OK, I know PHP doesn't have a compiler as such - but a static checker of some kind could work the same...)

gst• 12 years ago

https://en.wikipedia.org/wiki/Taint_checking

_pmf_• 12 years ago

Of note is that Perl had this since at least 1998. See http://gunther.web66.com/FAQS/taintmode.html

But of course we just laugh about Perl and pat ourself on our backs with our safe new languages because we clearly know much more than those anachronistic neckbeards.

deckiedan2• 12 years ago

Ah, "Taint" was the missing magic word I couldn't figure out to aid my google-fu (well, duckduckgofu...). Thanks for that - there is a lot of interesting stuff out there. :-)

adamnemecek2• 12 years ago

http://www.impredicative.com/ur/

riffraff• 12 years ago

perl and ruby have "taint" which is similar to what you describe.

And yes, this can be encoded in the type system and you can also make it so the sanitization is context dependent, i.e. http://www.comp.nus.edu.sg/~prateeks/papers/csas-ccs11.pdf

jonnyscholes• 12 years ago

PHP does to http://pecl.php.net/package/taint but I haven’t used it or the perl/ruby ones so I'm not actually sure how similar they are...

Argorak• 12 years ago

On the practical side, Ruby (MRI specifically) has such a system ($SAFE), that taints certain objects (e.g. those gained by IO) and only allows you to use them in certain fashions (e.g. only after explicit handling).

It's leaky as hell, because all components have to get the marking right. Also, not all Objects have equal trust levels. Objects created due to a HTTP request (GET-Parameters) should certainly be tainted, but how about Object read through IO - do we trust out filesystem? Do we trust the database? Thats more of an architectural decision.

In the end, the problem comes down to this: you have to whitelist the world and everything you miss is an error.

Morgawr• 12 years ago

There is Argos[0] which is a research project at my university, it's a qemu-based emulator that tracks tainted data coming from the network and other compromised sources and makes sure it doesn't tamper with memory or filesystem locations than it shouldn't. It's a bit overkill,especially for this, but it's interesting to check out :)

[0] http://www.few.vu.nl/argos/?page=1

MichaelGG• 12 years ago

Phantom types can help with this. F#'s unit of measurement does something similar for numbers.

zoomerang• 12 years ago

It's pretty easy to implement such a feature in any strongly typed language, but sadly few framework/libraries/stacks actually do it.

sltkr• 12 years ago

Then people notice that exec($_GET['foo']) doesn't work, but some smart cookie figures out that exec(untaint($_GET['foo'])) (or whatever the syntax is for removing the taint from an input variable) does, posts it online, and everyone copies that instead without thinking about the consequences.

slight• 12 years ago

PHP has a runtime taint checker module: http://www.php.net/manual/en/book.taint.php

chriswarbo• 12 years ago

Here's one approach: http://blog.moertel.com/posts/2006-10-18-a-type-based-soluti...

Different languages (SQL, JS, HTML, Shell, Plaintext, etc.) are treated as different types. Language-specific functions only accept arguments of the relevant type (eg. shell_exec takes Shell, db_query takes SQL, etc.). User input is Plaintext (usually; sometimes it might be something more specific like BASE64).

Different languages can't be combined (eg. SQL can't be concatenated with Plaintext), but they can be converted down to Plaintext and Plaintext can be converted to any language via escaping functions. This avoids injection attacks, since the only way to please the type-checker is by escaping properly.

shakesbeard• 12 years ago

https://wiki.php.net/rfc/taint

hashx• 12 years ago

Directly passing user data to the command line is highly dangerous.It allows an attacker to execute arbitrary commands on the command line [0]. escapehellarg [1] has to be used to Escape a string to be used as a shell argument

[0] http://gcattani.co.vu/2013/03/a-tale-of-a-php-shell/ [1] http://php.net/manual/en/function.escapeshellarg.php

fleitz• 12 years ago

Directly doing anything with attacker supplied data is generally a no-no.

Everything that may come from a user must be filtered, escaped or generally treated as hostile.

As an example on an IRC channel someone once made their chan bot log the channel to the web, all it took was pasting javascript into an IRC window, and typing "LOL look at this! http://stupidbot.com/ircweblog". Channel pwned.

rallemoose• 12 years ago

Meet his brother https://github.com/search?q=eval%28%24_GET&type=Code&ref=sea... (eval($_GET

lauriswtf• 12 years ago

Also relevant - https://github.com/search?q=mysql+%24_GET&type=Code&ref=sear...

bowlofpetunias• 12 years ago

The names of the files alone suggests many of these are quite deliberate.

elwell2• 12 years ago

most of those are demonstrations of the vulnerability

nathancahill• 12 years ago

Note that most of these are intentional. pointer.jpg.php, pypwn/test.php, w3af-moth, etc.

VMG2• 12 years ago

Are there any more sophisticated parses that also find the non-obvious cases?

It should be easily doable to write a tool that finds an exec() of a variable that was assigned a $GET etc

theon144• 12 years ago

I think it's easier to just avoid exec() altogether...

VMG2• 12 years ago

True, but there is a lot of software out there where people don't do that. Might be interesting to find vulnerabilities that are slightly less obvious.

Xylakant• 12 years ago

Sadly, there's cases where exec() is impossible to avoid - for example, every kind of tool that doesn't have a proper library and language bindings. See git and the grit library for an example.

WestCoastJustin• 12 years ago

As a side note, this is how many SQL injection attacks happen too. You almost never want unfiltered user input to directly interact with your system. A while back, I did an episode on how SQL injection can lead to code execution by using unfiltered user input on a LAMP stack. See it @ http://sysadmincasts.com/episodes/21-anatomy-of-a-sql-inject...

ASneakyFox3• 12 years ago

Side side note. This same carelessness is what caused the heart bleed bug.

Kim_Bruning• 12 years ago

Well, in a sense maybe, but not on purpose there. The programmer had missed a bounds check.

mattwritescode• 12 years ago

Thats a little more than concerning!

ephemeralgomi• 12 years ago

This is awful. Shell commands are not guaranteed to be idempotent, people! These should all be of the form exec($_POST, not exec($_GET.

RutZap3• 12 years ago

I think the problem here is the fact that tainted variables (user input) are used to execute shell commands. it doesn't matter if that's $_POST or $_GET, both of these are user input and therefore these are huge vulnerabilities.

saurik• 12 years ago

"That's the joke."

masklinn• 12 years ago

I'm pretty sure GP was being sarcastic.

huseyinkeles• 12 years ago

I think he is being sarcastic.

oleganza• 12 years ago

I think he was indeed sarcastic.

gnurag• 12 years ago

I think he is indeed being sarcastic.

cassm• 12 years ago

I think he is was being indeed sarcastic.

kvcrawford• 12 years ago

I'm sorry, but I can't hear you over the sound of the joke flying overhead.

izietto4• 12 years ago

It depends by the command, echo is idempotent for example. There should be some checking like

  $cmdname = split(' ', $_GET['command']);
  if(!in_array(IDEMPOTENT_COMMANDS, $cmdname))
     echo '<h1>Your request is not guaranteed to be idempotent. Please use a POST.</h1>';
  else
    exec($_GET['command'] ...

TeMPOraL• 12 years ago

    if(!in_array(IDEMPOTENT_COMMANDS, $cmdname)) {
     header("HTTP/1.1 405 Method Not Allowed");
     die();
     }

Fixed ;).

dspillett• 12 years ago

  echo is idempotent

As a simple call, yes. But there are many shell tricks (redirection, command substitution, process substitution) that can make an echo call have significant side effects - so if you were daft enough to be considering this you'd need to do much more checking before submitting the provided instruction to your shell, and those checks would need to know which shell you were targeting (in fact you'd probably want to force the issue by exec()ing a specific shell instead of just using the default for the user the code is running as).

RoryH• 12 years ago

Love the sarcasm ;-)

venomsnake• 12 years ago

I prefer exec($_REQUEST when I have to do something like that. You capture both get and post variables.

chriskottom• 12 years ago

  88,846  PHP
   1,420  HTML+ERB
   1,177  JavaScript
   1,128  HTML
     423  Ruby
     250  XML
     160  Markdown
     117  Emacs Lisp
      91  INI
      65  Perl

catkin• 12 years ago

Not actually so surprising considering `$_GET` is a PHP superglobal.

sprobertson• 12 years ago

Though I'm surprised how many aren't PHP, for example all the Ruby repos...

Edit: ah, most of those are Metasploit scripts.

devsmt• 12 years ago

try "exec params" and "call request" for shooting your foot in other languages

jafingi• 12 years ago

This seems pretty secure.. https://github.com/searchmanipulator/missteencincinnati/blob...

DanOWar• 12 years ago

Example from the Github search:

     <?php
          $result=shell_exec("cat ".$_GET['name'].".txt");
          echo $result;
     ?>

How to abuse:

     $_GET['name'] = "/dev/null; rm -rf /; echo ";

xikrib• 12 years ago

need root access, no?

LeonM• 12 years ago

Thats not the point. Of course "rm -rf /" won't work, but what about downloading and installing a backdoor? Or modifying the website scripts itself? Or dumping a database? Or...

Removing all the files from a filesystem is something only a script kiddy would do, and it's probably a "best case scenario" for the owner of the server, because the impact of that is relatively small (just re-install the server and restore the backups). But once the attacker starts injecting mallware, stealing customer information (credit card numbers anyone?) or anything else nasty they can think of that they would benefit from, then you are in a whole lot more trouble...

skriticos2• 12 years ago

True, but once you have <foo; $any_command_with_user_privilege> you can start executing any user commands. So you do a </dev/null; mkdir ~/www/nefarious; cp ~/www/AdminSettings.php ~/www/nefarious/settingns.txt;> (without the index file you can just view the file as plain text, which probably contains the database username and password. Then you can go on and download a database dump. The attacker probably does not give a damn about root in this scenario.

izietto4• 12 years ago

Wrong. `rm -rf /` fails without the `--no-preserve-root` option.

moloch• 12 years ago

'rm -rf /*' should do the trick; kind enough to leave them with a '/' directory.

dkarapetyan• 12 years ago

Half the time these are just prototypes or throwaway projects or are behind password protected proxies. Relax people.

voltagex_3• 12 years ago

Paul's Security Weekly (a security podcast) had their blog owned after inadvertently removing the .htaccess (the password protection in your example) from their admin directory.

ASneakyFox3• 12 years ago

I'm sure he quickly loss viewership as a result too.

brianbarker• 12 years ago

My fav:

$device = $_GET['device']; $state = $_GET['state'];

exec( "sudo ./send " . $device . " " . $state );

EDIT: it is for home automation, but also appears to be a CS class group project.

voltagex_3• 12 years ago

I really, really, really want to post on their issue tracker, but maybe I shouldn't. There's no guarantee the person grading the project will care, either.

marlin4• 12 years ago

You should. But be factual. No point in bringing the attitude.

blueskin_3• 12 years ago

How about one with root access included?

https://github.com/search?q=exec+sudo+%24_GET&type=Code&ref=...

nacs• 12 years ago

Fortunately looks like most of those are home-automation/maintenance scripts.

hellerbarde2• 12 years ago

Fortunately?? More often than we all care to admit, these things are exposed to the internet. (because it's so cool when I can turn on the coffee machine from my smartphone halfway home from work)

tlrobinson2• 12 years ago

I admit I wrote some not-dissimilar PHP code when I was about 15 :-/

pgl• 12 years ago

This needs to be quoted to return decent results:

https://github.com/search?q=%22exec%28%24_GET%22&type=Code&r...

Otherwise there are way too many false positives. Still, 188 results is pretty awful.

marlin4• 12 years ago

You now also excluded thousands of true positives which dont present the code exactly as queried

bananas2• 12 years ago

I already have a thing called "all seeing eye" that picks up on things like this on a pre-commit script in SVN and tells people to go away if they do something stupid. It's done some wonderful work so far.

marlin4• 12 years ago

Horrible.. Been sending 2 security bug reports so far.

sathio• 12 years ago

<?php

$_GET['a']($_GET['b']);

homakov• 12 years ago

So what? Vulnerability in random noname website worth approx. $0

ultrafez• 12 years ago

I thought this one[0] was a little ironic - it's part of the codebase for a vulnerability management system.

[0] https://github.com/riflon/Timantti/blob/2459c44fde2b378f63ac...

tizoc• 12 years ago

Another one with even more results: https://github.com/search?q=eval%28%24_GET&type=Code&ref=sea...

drtse4• 12 years ago

Did someone else notice that that github search returns mostly results where exec is completely disconnected by $_GET? And that, i'd say, the last 20 pages contain the same thumbnail script that contains simply the "exec" string and multiple uses $_Get somewhere?

Maybe it's still an asinine error somewhat common, but i wouldn't take that search results as proof of how common it is...

mnicky• 12 years ago

Just use quotes then. Actually, it seems that $_POST is a little bit more common ;)

https://github.com/search?q=%22exec%28%24_POST%22&type=Code

vs.

https://github.com/search?q=%22exec%28%24_GET%22&type=Code

jayzalowitz• 12 years ago

https://github.com/search?q=%22exec%28%24_GET%22&type=Code&r...

is more the point you were trying to make, but yes.

grhmc• 12 years ago

Let's just fix them: http://www.cng.edu/files/pointer.jpg.php?shak=rm%20pointer.j...

mback2k• 12 years ago