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Original issue date: October 17, 1991<Br>
Last revised: September 18, 1997<BR>
Attached copyright statement

<P>A complete revision history is at the end of this file.

<P>The Computer Emergency Response Team/Coordination Center (CERT/CC) has
received information concerning a vulnerability in the TFTP daemon in
all versions of AIX for IBM RS/6000 machines.

<P>IBM is aware of this problem and a fix is available as apar number "ix22628".
This patch is available for all AIX releases from "GOLD" to the current
release.

<P>NOTE: THIS IS AN UPDATED PATCH FROM ONE RECENTLY MADE AVAILABLE and fixes
a security hole in the original patch.  The SCCS id of the correct patch
is tftpd.c 1.13.1.3 (*not* 1.13.1.2 or earlier versions).  This can be 
checked using the following "what" command.
<PRE>
    % what /etc/tftpd
    /etc/tftpd:
    56      1.13.1.3  tftpd.c, tcpip, tcpip312 10/10/91 09:01:48
    tftpsubs.c      1.2  com/sockcmd/tftpd,3.1.2,9048312 10/8/89 17:40:55
</PRE>

IBM customers may call IBM Support (800-237-5511) and ask that the fix
be shipped to them.  The fix will appear in the upcoming 2009 update
and the next release of AIX.

<P>
<HR>
<H2>I. Description</H2>


Previous versions of tftpd did not provide a method for restricting 
TFTP access.

<H2>II. Impact</H2>


If TFTP is enabled at your site, anyone on the Internet can retrieve
copies of your site's world-readable files, such as /etc/passwd.

<H2>III. Solution</H2>

<H3>A. Sites that do not need to allow tftp access should disable it.</H3>

This can be done by editing /etc/inetd.conf and deleting or
commenting out the tftpd line:
<PRE>
#tftp     dgram     udp    wait    nobody  /etc/tftpd     tftpd -n
</PRE>
and then, as root, restarting inetd with the "refresh" command.
<PRE>
# refresh -s inetd
</PRE>
For more details on starting/stopping tftp, refer to documentation
for the System Resource Controller (SRC) or the System Management
Interface Tool (SMIT).

<H3>B. Sites that must run tftpd (for example, to support X terminals) 	should obtain and install the above patch AND create a /etc/tftpaccess.ctl file to restrict the files that are accessible.</H3>
The /etc/tftpaccess.ctl file should be writable only by root.
Although the new /etc/tftpaccess.ctl mechanism provides a very general
capability, the CERT/CC strongly recommends that sites keep this
control file simple.  For example, the following tftpaccess.ctl file
is all that is necessary to support IBM X terminals:
<PRE>
	# /etc/tftpaccess.ctl
        # By default, all files are restricted if /etc/tftpaccess.ctl exists.
	# Allow access to X terminal files.
          allow:/usr/lpp/x_st_mgr/bin
</PRE>
	NOTE: Be CERTAIN to create the /etc/tftpaccess.ctl file.<BR>
If it does not exist then all world-readable files are accessible
as in the current version of tftpd.

<P>Installation Instructions:
<OL>
<H4><LI>        Create an appropriate /etc/tftpaccess.ctl file.</H4>

<P>
<H4><LI>  From the directory containing the new tftpd module, issue  the following commands as root.</H4>
        <PRE>
            # chmod 644 /etc/tftpaccess.ctl
            # chown root.system /etc/tftpaccess.ctl
	    # mv /etc/tftpd /etc/tftpd.old
	    # cp tftpd /etc
	    # chmod 755 /etc/tftpd
	    # chown root.system /etc/tftpd
            # refresh -s inetd
</PRE>

</OL>
<HR>

<P>The CERT/CC wishes to thank Karl Swartz of the Stanford Linear Accelerator
Center for bringing this vulnerability to our attention.

<!--#include virtual="/include/footer_nocopyright.html" -->
<P>Copyright 1991 Carnegie Mellon University.</P>

<HR>

Revision History
<PRE>
September 18,1997  Attached Copyright Statement
</PRE>