Tuesday, February 25, 2014

Codegate CTF 2014 - Web Proxy - Web 200 Write-up

In this challenge we were given a proxy and in the html source code
a commented line which states:
admin/index.php
it was clear that we should get into that file when we tried to get it from outside
it gave an 403 forbidden error and when you try to get it from inside with exact link
it was giving Access Denied response. So we figure out that the proxy was
processing the url you requested and if it is containing one of the "php" or "//"
it was giving that Access Denied response so we requested the page with just
localhost/188f6594f694a3ca082f7530b5efc58dedf81b8d/admin/
which should give the default index and it worked but the response wast trimmed
we could get just a few lines and we thought that there might be a vuln in
request that proxy making so i just put the and of the link a %0a which is \n
and ta-daa the headers were gone we got just the contents of the page something
went absolutely wrong. When i examined deeply i see that the proxy is working by
putting the url we requested directly into the request so:

GET "our_url" HTTP/1.1
Host: xxx
And other headers.
.
.
.

the get request was happening that way so i manipulated it by hand to use
Range header it allows us to seek to any wanted byte of the file so i gave an
url like

localhost/188f6594f694a3ca082f7530b5efc58dedf81b8d/admin/ HTTP/1.1%0d%0aHost:localhost%0d%0aRange:bytes=380-%0d%0a%0d%0a

and the output was checking if the host is "hackme" so i changed my host line
and rearrangen range field for new file to get the password like this:

localhost/188f6594f694a3ca082f7530b5efc58dedf81b8d/admin/ HTTP/1.1%0d%0aHost:hackme%0d%0aRange: bytes=70-%0d%0a%0d%0a

and ta-daa there is the password.

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