1. Copy the content of theĀ <TITLE> tag from advisories/CA-YYYY-NN.html to the page title above.
  2. Copy the entire content of the corresponding file from body/advisories/CAYYYYNN_FAYYYYNN.html into the HTML box below.
  3. (optional) Delete this page properties box prior to saving. This step is optional because it won't display on the rendered page anyway, only in edit mode.
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

a security hole in the original patch.  The SCCS id of the correct patch
is tftpd.c (*not* or earlier versions).  This can be 
checked using the following "what" command.
    % what /etc/tftpd
    56  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

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.

<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:
#tftp     dgram     udp    wait    nobody  /etc/tftpd     tftpd -n
and then, as root, restarting inetd with the "refresh" command.
# refresh -s inetd
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:
	# /etc/tftpaccess.ctl
        # By default, all files are restricted if /etc/tftpaccess.ctl exists.
	# Allow access to X terminal files.
	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:
<H4><LI>        Create an appropriate /etc/tftpaccess.ctl file.</H4>

<H4><LI>  From the directory containing the new tftpd module, issue  the following commands as root.</H4>
            # 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


<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>


Revision History
September 18,1997  Attached Copyright Statement