Avoiding EVAL()
There are a shed-load of ways to “eval()” code without actually calling the eval() function — usually done simply to avoid the use of the dreaded “evil()” function, but often times because the system has eval() disabled using “disable_functions” in php.ini
Here is another simple way to avoid eval() without writing out files to the filesystem etc:
<?php
$code = '<?php echo "Hello World"; ?>;
include('data:text/plaintext;base64,' . base64_encode($code));
?>
This uses the new data: stream wrapper (RFC2397) that was introduced with PHP 5.2.0; and while this seems like a risk, first: The “attacker” already has access to the code on your system, or you’re open to injection anyway, second: PHP 5.2 has also fixed the problem with the introduction of the ”allow_url_include” php.ini option.
I just thought it was a neat little streams “hack” I would share; I originally thought to do it using the var stream from PHP’s stream_wrapper_register() documentation, but then Evert Pot posted about creating streams from strings using the data: stream, which led to this final “solution”.
- Davey
12 Responses to “Avoiding EVAL()”
@JillyEnFuego it's where they pretend a bunch of folks survived the apocalypse and what they have to do to survive; reality style
@dshafik [1 day ago]
@dshafik Oooh! See that's why I have to DVR things, I can't keep up with when shows come on.
@tattooedmommie [1 day ago]
@tattooedmommie it started last night...
@dshafik [1 day ago]
@dshafik hahahaha.. doesn't everyone?
@beth_warren [1 day ago]
@david973 I've known her 14 years; so I'm not far behind :P
@dshafik [1 day ago]

















Nice piece of information, thanks. However, I think either you’re wrong or I understood you wrong, but allow_url_include directive has been available since 5.1.
As Johannes pointed out, it was also added in 5.2; it was a typo on my part
Yes, I’ve re-checked it, and it seems it was introduced in 5.2, not in 5.1 as I previously posted.
allow_url_include is no 5.3 but 5.2 introduced feature, data: was no “URL Stream” for one or two versions of that series, but that was fixed soon to avoid troubles like the one above
Silly and completely useless. I don’t see an serious use case for this “feature”.
I never claimed it was useful. And there certainly is no *serious* use case; I just enjoy bending the language
There’s a lot of pay scripts that are eval base64 encoded.. Could use this to no use eval.. Still insecure.
man… and I thought I wrote sinister code! Thanks for sharing, Davey.
[...] Avoiding EVAL() (tags: PHP) [...]
Lookie:
http://pastebin.com/f6662eb57
eval() is significantly faster than include() – on my computer it’s a difference of about 35%.
This is quite obvious; there is a base64_encode() and a base64_decode() involved in my solution. However, benchmarks in userland are inherently flawed.
On the other hand this shows a nice exploit when eval is disabled. You could easily inject your code to execute by exploiting a bug with dynamic variable includes.