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Subject: Zeus Web Server: Null Terminated Strings
From: Julian Midgley (jmidgleyZEUSTECHNOLOGY.COM)
Date: Tue Feb 08 2000 - 06:49:04 CST
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This morning Zeus Technology Limited was informed of a serious security
bug in the Zeus Webserver by 'The Relay Group' (http://relaygroup.com).
This document describes the scope of the problem and its solution.
Zeus 3.1.x / 3.3.x
High- this bug allows the contents of CGI scripts to be read by a remote
client, if the scripts are run with the CGI module's "allow CGIs
anywhere" option enabled.
It does not affect CGIs run from designated directories (cgi-bins).
Nonetheless, we recommend that all customers upgrade to Zeus 3.3.5a- see
below for further details.
Requests for URLs which contains the text '%00' are decoded to contain
a null-terminator. This means that files can be accessed via URLs
that are not access controlled, allowing files that are *inside* the
document root to be retrieved.
For example, if you run a webserver with the 'allow CGI anywhere' option,
and have a Perl CGI script inside the document root accessible as
'http://mysite/script.cgi' then a request for
'http://mysite/script.cgi%00' will cause the webserver to return the Perl
source of the CGI script to the client.
This happens because the mime-type of '.cgi\0' does not map to
'application/x-httpd-cgi', so is instead served by the get module as
'text/plain'. The webserver will ask the OS for the file
'script.cgi\0\0', and due to the zero-terminated string interface of
Unix, the OS will actually open 'script.cgi\0' instead of returning a
We have fixed the problem in the latest version of Zeus (3.3.5a) now
available for all 14 platforms from our ftp site
This version will report itself as '3.3.5a' and also
display today's (8th Feb) date on startup.
Download the distribution for your platform, untar it, and run
'./zinstall --force' and it will seamlessly upgrade your running
server to the fixed release.
-- Julian Midgley Tel: +44 1223 525000 Technical Services Manager Fax: +44 1223 525100 Zeus Technology Ltd http://www.zeustechnology.com Newton House, Cambridge Business Park, Cambridge. CB4 OWZ. England