JRun SSI Request Body Parsing

[Netcraft Security <security () netcraft com>]

Vulnerable Products:  JRun Java application server from Allaire. All
                      current versions (with latest security patches as
                      of November 2001) are believed to be affected,
                      including 2.3.3, 3.0, and 3.1.

Impact:               Revealing of source code to Java Server Pages,
                      and other protected files inside the web root.

Affects:              Web sites using vulnerable products as stated above

Revision history:     Vendor notified: 22nd October, 2001
                      Initial security bulletin created: 23rd October, 2001
                      Vendor workaround released: 27th November, 2001
                      Security bulletin published: 28th November, 2001

The latest version of this advisory is available at:
http://www.netcraft.com/security/public-advisories/2001-11.1.html

Overview

JRun supports a number of different technologies for dynamically
generated content, most importantly Java Server Pages. One lesser-used
feature is the support for Server Side Includes (SSI); this is a much
simpler language than JSP, which is primarily for including the text of
other files on the server (for instance adding standard headers or
footers to otherwise static pages), and also supports invoking servlets.
By default, the file extension .shtml is assigned to the SSI handler.

Unfortunately, a flaw in the server side component that processes
requests for SSI pages means that user supplied data can be included in
the SSI processing. A remote user can submit requests containing data
which will be processed by the SSI filter; as a result the user can
cause the server to execute arbitrary SSI code.

Details

When a request for an SSI page is submitted to the server, and the page
does not exist, the SSI handler "falls back" on the body of the HTTP
request itself. Usually an HTTP request does not contain a body, but a
malicious user can easily construct a request with a body containing SSI
commands. These can be used to include the source to other files on the
server. For example, a request such as:

GET /nosuch.shtml HTTP/1.0
Content Length: 38

<!--#include virtual="/index.jsp"-->

would return the source of the index.jsp page (subject to SSI processing
- so servlet tags may be replaced, but most JSP source would be passed
through unmodified). It should be noted that the include directive does
not go through the usual URL processing - for example includes of .jsp
files are not done by the JSP handler, hence the source code to .jsp's
can be obtained. It also bypasses any access controls enforced by the
web server (so files in protected directories such as the /WEB-INF/
directory can be accessed). However, it was not possible to access files
outside of the web root in the cases that Netcraft tested.

Netcraft also verified that it was possible to execute Java servlets on
the server using this vulnerability. As it is common to expose these via
the /servlet/ URL mapping, this does not give the attacker any new
advantage in the normal setup but could be considered a problem by sites
that have disabled the /servlet/ mapping.

Recommendations

As a workaround, sites using JRun can disable the SSI support on the web
server, as this is not required for any other features of the server
including Java Server Pages, so few sites actually require this
functionality. This involves both disabling the .shtml extension mapping
to SSI handling, and the /servlet/ method of invoking the servlet which
does SSI processing (the latter can be done by either disabling the
/servlet/ mapping if it is not used, or by blocking access to the
particular servlet affected - allaire.jrun.ssi.SSIFilter for JRun 3.x,
com.livesoftware.jrun.plugins.ssi.SSIFilter on JRun 2.3.x). See the
security bulletin from Allaire for detailed information on making this
configuration change.

Vendor Patches and Comments

Allaire have responded promptly to Netcraft's initial report of this
problem. They have confirmed that this is a security problem in the JRun
versions listed. A patch is expected to be included in the next rollup
patch for JRun. In the meantime they have released a security bulletin
at http://www.allaire.com/handlers/index.cfm?ID=22235&Method=Full to
notify customers of this problem, and advise a workaround by disabling
SSI.

Disclaimer

This information is provided on an AS IS basis in the hope that it is
useful in securing vulnerable computer systems; however Netcraft cannot
guarantee its accuracy or accept responsibility for any damage resulting
from the release of this advisory.

Netcraft

This is one of many vulnerabilities tested by Netcraft's security testing
services. Please see http://www.netcraft.com/security/ for more
information.

(c) Netcraft 2001 - May be reproduced or quoted provided Netcraft and the
URL http://www.netcraft.com/security/ are attributed.