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SNI-16: INN News Server Security Advisory
From: sni () SILENCE SECNET COM (Secure Networks Inc.)
Date: Mon, 21 Jul 1997 14:47:50 -0600


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                           Secure Networks Inc.

                            Security Advisory
                              July 21, 1997

                     INN news server vulnerabilities

This advisory addresses a number of vulnerabilities present in all
versions of INN prior to version 1.6.


Problem Description:
~~~~~~~~~~~~~~~~~~~~

A number of vulnerabilities exist in all versions of INN prior to
version 1.6 which allow remote individuals to obtain access to
vulnerable systems.  Post access is required to exploit these
vulnerabilities.  However, due to the method with which news is
propagated, once a single server has been broken into, all of its
peers can be accessed.


Technical Details:
~~~~~~~~~~~~~~~~~~

A number of string copies within the INN news server fail to check
the size of data they are copying.  This results in buffer overflows
in several locations, allowing individuals to execute commands
remotely, including spawning a shell on the NNTP port.

An example of this situation is in the processing of the "From: "
line by the nnrpd process.  In the ARTpost function in post.c, the
From: line is copied into a buffer on the stack without performing
bounds checking:

STRING
ARTpost(article, idbuff)
    ...
    char                buff[NNTP_STRLEN + 2], frombuf[SMBUF];
    ...
    strcpy(frombuf, HDR(_from));
    ...

By crafting appropriate arguments in the From: header of the message,
an attacker can cause nnrpd to overwrite its stack, overwrite
the function return pointer on the stack, and thus execute arbitrary
binary code.


Vulnerable Operating Systems and Software
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

All versions of INN prior to version 1.6 are vulnerable.  To determine
which version of INN you are running, issue the following command on
your news server:

% telnet localhost 119

Your NNTP server version string will be displayed.  A typical output from
a vulnerable NNTP server would read:

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
200 freebsd.secnet.com InterNetNews NNRP server INN 1.5.1 17-Dec-1996 ready

A line reading:

telnet: Unable to connect to remote host: Connection refused

means that you are not running an NNTP server.


Fix Information
~~~~~~~~~~~~~~~

INN version 1.6 has been made availible at ftp://ftp.isc.org/isc/inn.  A
fix will not be made availible for prior releases and it is suggested that
all users running INN upgrade to version 1.6 immediately.

Please note that INN version 1.6 is currently in beta testing stages,
therefore new versions may appear at this location in the future.


Additional Information
~~~~~~~~~~~~~~~~~~~~~~

Secure Networks Inc. wishes to thanks James Brister <brister () isc org> for
his assistance in this advisory and a resolution to these problems.

You can contact Secure Networks Inc. at <sni () secnet com> using the
following PGP key:

Type Bits/KeyID    Date       User ID
pub  1024/9E55000D 1997/01/13 Secure Networks Inc. <sni () secnet com>
                              Secure Networks <security () secnet com>

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You can find past Secure Networks advisories at
http://www.secnet.com/advisories or at ftp://ftp.secnet.com/pub/advisories

You can browse our web site at http://www.secnet.com

You can subscribe to our security advisory mailing list by sending
mail to majordomo () secnet com with the line "subscribe sni-advisories"


Copyright Notice
~~~~~~~~~~~~~~~~

The contents of this advisory are Copyright (C) 1997 Secure Networks
Inc, and may be distributed freely provided that no fee is charged
for distribution, and that proper credit is given.


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