protecting file upload

Hi,

I've read a few bits on the web about vulnerabilities in providing
file uploads where the upload could contain ../../ and so allow 'back
browsing' to other files on the server and copying them to a public
directory. If I was to check for this scenerio, would I have to do
something like (in simple terms):

if $_FILES['userfile']['tmp_name'] or $_FILES['userfile']['name'] =
.../../
echo u are norty
else
continue with code

Also, is it possible to verfiy that the referring html form to my
upload script originates from my server only? I could stop anyone from
creating their own forms then.

Many thanks

ahevans@gmail.com (ahevans) wrote in news:d589c3f.0502120410.15a672d7
@posting.google.com:
[color=blue]
> Hi,
>
> I've read a few bits on the web about vulnerabilities in providing
> file uploads where the upload could contain ../../ and so allow 'back
> browsing' to other files on the server and copying them to a public
> directory. If I was to check for this scenerio, would I have to do
> something like (in simple terms):
>
> if $_FILES['userfile']['tmp_name'] or $_FILES['userfile']['name'] =
> ../../
> echo u are norty
> else
> continue with code[/color]

See:

<http://groups-
beta.google.com/group/comp.lang.php/browse_frm/thread/eff851f20fb4a8d/af5ad
51cf5946e1c>

(URL should all be on one line. Hey Google, new groups.google blows.)
[color=blue]
> Also, is it possible to verfiy that the referring html form to my
> upload script originates from my server only? I could stop anyone from
> creating their own forms then.[/color]

It's possible to detect the referring URL, but anyone can send whatever
Referer header they choose. There is no real security in checking the
Referer header.

hth


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