[UNIX] Yaws Webserver Code Disclosure

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Yaws Webserver Code Disclosure
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SUMMARY

<http://yaws.hyber.org> Yaws is "a HTTP high performance 1.1 web server.
Yaws is entirely written in Erlang furthermore it is a multi-threaded web
server where one Erlang light weight process is used to handle each
client".

Yaws server discloses the script's source whenever a NULL byte is appended
to scripts filename.

DETAILS

Vulnerable Systems:
* Yaws versions 1.55 and prior

Immune Systems:
* Yaws versions 1.56

If a NULL byte is appended to the filename of a yaws script (.yaws), the
yaws web server will return the page containing the source code of the
according script. This flaw allows a malicious attacker to analyze the
source code of the entire web application, which might result in the
attacker gaining sensitive information like passwords.

The yaws homepage itself was vulnerable to the attack. Opening the link
http://yaws.hyber.org/dynamic.yaws%00 in a browser resulted in the display
of the following code (only the first couple of lines...):

<erl>
box(Str) ->
{'div',[{class,"box"}],
{pre, [], yaws_api:htmlize(Str)}}.

tbox(T) ->
box(lists:flatten(io_lib:format("~p",[T]))).

..

Disclosure Timeline:
16.06.05 - Vendor notified
16.06.05 - Vendor response
16.06.05 - Patch available

Vendor Status:
Vendor was extremely fast to response and post a fix. You can download a
patch from: <http://yaws.hyber.org/yaws-1.55_to_1.56.patch>
http://yaws.hyber.org/yaws-1.55_to_1.56.patch

ADDITIONAL INFORMATION

The information has been provided by <mailto:research@sec-consult.com>
Daniel Fabian.
The original article can be found at:
<http://www.sec-consult.com/181.html> http://www.sec-consult.com/181.html

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