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IBM SECURITY ADVISORY
 
First Issued: Wed Jul  6 08:38:14 CDT 2005
 
=========================================================================
                           VULNERABILITY SUMMARY
 
VULNERABILITY:      A denial of service vulnerability in ftpd
 
PLATFORMS:          AIX 5.1, 5.2 and 5.3.
 
SOLUTION:           Apply the workaround, interim fix or APARs as
                    described below.
 
THREAT:             A remote user may cause performance degradation
                    or a denial of service.
 
CERT VU Number:     VU#118125
CVE Number:         N/A
=========================================================================
                           DETAILED INFORMATION
 
 
I.  Description
===============
 
The ftpd daemon provides the server function for the FTP protocol which
allows files to be transfered between two hosts. A vulnerability has been
found in ftpd which allows a remote user to cause a denial of service by
using all available ephemeral ports. This in turn will cause ftpd to
allocate an amount of memory for sockets which is disproportionate to what
it typically uses. Of these two issues, using all available ephemeral
ports and using more memory for sockets, the former poses a greater threat
because those ports will not be available to be used for other purposes.
 
This issue can be exploited by any user which can authenticate with ftpd.
If the system is configured to use anonymous ftp, the anonymous ftp user
can also exploit this vulnerability.
 
ftpd ships as part of the bos.net.tcp.client fileset. To determine if this
fileset is installed, execute the following command:
 
# lslpp -L bos.net.tcp.client
 
If the fileset is installed it will be listed along with its version
information, state, type and a description.
 
 
II. Impact
==========
A remote user may cause a denial of service or performance degradation.
 
III.  Solutions
===============
 
A. Official Fix
 
IBM provides the following fixes:
 
      APAR number for AIX 5.1.0: IY73498 (available approx.  09/07/05)
      APAR number for AIX 5.2.0: IY72942 (available approx.  09/05/05)
      APAR number for AIX 5.3.0: IY73497 (available approx.  09/05/05)
 
NOTE: Affected customers are urged to upgrade to 5.1.0, 5.2.0 or 5.3.0 at
the latest maintenance level.
 
B. Interim Fix
 
Interim fixes are available for AIX 5.1.0, 5.2.0 and 5.3.0. The ifixes can
be downloaded via ftp from:
 
    ftp://aix.software.ibm.com/aix/efixes/security/ftpd_ifix.tar.Z
 
ftpd_ifix.tar.Z is a compressed tarball containing this advisory, three
ifix packages and cleartext PGP signatures for each package.
 
 
Verify you have retrieved the ifixes intact:
- - --------------------------------------------
The checksums below were generated using the "sum" and "md5sum" commands
and are as follows:
 
Filename                  sum         md5
======================================================================
IY73498_08.050701.epkg.Z  47978    94 0c92b7aae0c12b5779240d2a4dceeb26
IY72942_04.050701.epkg.Z  46458   104 c2cbf1618dad82ff621d5a28e2b1ff67
IY72942_05.050701.epkg.Z  37293   104 8482fcac5b46a191954ed163f9ed811f
IY72942_06.050701.epkg.Z  36063   104 6c9951a0fa5de3bc87179949c550669c
IY73497_01.050701.epkg.Z  51428   110 75f9ed3994ff69502ce552f2023f0249
IY73497_02.050701.epkg.Z  39327   110 e1872c5e87244e3b723ae58549adba9f
 
 
These sums should match exactly. The PGP signatures in the compressed
tarball and on this advisory can also be used to verify the integrity of
the various files they correspond to. If the sums or signatures cannot be
confirmed, double check the command results and the download site address.
If those are OK, contact IBM AIX Security at security-alert@austin.ibm.com
and describe the discrepancy.
 
IMPORTANT: If possible, it is recommended that a mksysb backup of the
system is created. Verify it is both bootable, and readable before
proceeding.
 
These ifixes have not been fully regression tested; thus, IBM does not
warrant the fully correct functioning of the ifix.  Customers install the
ifix and operate the modified version of AIX at their own risk.
 
Interim Fix Installation Instructions:
- - --------------------------------------
These packages use the new Interim Fix Management Solution to install
and manage ifixes. More information can be found at:
 
     http://techsupport.services.ibm.com/server/aix.efixmgmt
 
To preview an epkg ifix installation execute the following command:
 
# emgr -e ipkg_name -p       # where ipkg_name is the name of the
                             # ifix package being previewed.
 
To install an epkg ifix package, execute the following command:
 
# emgr -e ipkg_name -X       # where ipkg_name is the name of the
                             # ifix package being installed.
 
The "X" flag will expand any filesystems if required.
 
Before the ifix is installed, ftpd should be stopped and once the ifix is
installed, it should be started again. By default the following command
can be used to stop ftpd:
 
# stopsrc -t ftp             # note that this will terminate
                             # current ftp connections.
 
The following command can be used to start ftpd:
 
# startsrc -t ftp
 
C. Workaround
 
There are several steps which can be taken to mitigate the risk posed by
this vulnerability:
 
1. Turn ftpd off if it is not needed. 
2. Do not allow anonymous FTP. A user with a valid username and password
   will still be able to exploit these issues but anonymous FTP users will
   not be able to.
3. Set the system wid network option "sockthresh" such that it will not
   consume a substantial amount of system memory. The appropriate value
   depends on the system in question.
4. Use the system wide network options "tcp_ephemeral_low" and
   "tcp_ephemeral_high" to specify a range of ephemeral ports. This will
   limit the range of ephemeral ports for the entire system. While this
   will not prevent a ftpd from using all available ephemeral ports, it
   will limit the amount of system resources that ephemeral ports can
   consume. 
 
 
IV. Obtaining Fixes
===================
AIX Version 5 APARs can be downloaded from:
 
     http://www-1.ibm.com/servers/eserver/support/pseries/aixfixes.html
 
Security related Interim Fixes can be downloaded from:
 
     ftp://aix.software.ibm.com/aix/efixes/security
 
 
V.  Contact Information
========================
 
If you would like to receive AIX Security Advisories via email, please
visit:
    https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs
 
Comments regarding the content of this announcement can be directed to:
 
     security-alert@austin.ibm.com
 
To request the PGP public key that can be used to communicate securely
with the AIX Security Team send email to security-alert@austin.ibm.com
with a subject of "get key". The key can also be downloaded from a PGP
Public Key Server. The key id is 0x9391C1F2.
 
Please contact your local IBM AIX support center for any assistance.
 
eServer is a trademark of International Business Machines Corporation.
IBM, AIX and pSeries are registered trademarks of International Business
Machines Corporation. All other trademarks are property of their
respective holders.
 
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