Summary

Vulnerability in OpenSSH affects AIX.

Vulnerability Details

CVEID: CVE-2018-15473 DESCRIPTION: OpenSSH could allow a remote attacker to obtain sensitive information, caused by different responses to valid and invalid authentication attempts. By sending a specially crafted request, an attacker could exploit this vulnerability to enumerate valid usernames.
CVSS Base Score: 5.3
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/148397&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

Affected Products and Versions

AIX 5.3, 6.1, 7.1, 7.2
VIOS 2.2.x

The following fileset levels are vulnerable:

key_fileset = osrcaix

Fileset Lower Level Upper Level KEY
-------------------------------------------------------------
openssh.base.client 4.0.0.5200 7.5.102.1500 key_w_fs
openssh.base.server 4.0.0.5200 7.5.102.1500 key_w_fs

Note: To determine if your system is vulnerable, execute the following commands:

lslpp -L | grep -i openssh.base.client
lslpp -L | grep -i openssh.base.server

Remediation/Fixes

A. FIXES

Fixes are available. The fixes can be downloaded via ftp and http from:

ftp://aix.software.ibm.com/aix/efixes/security/openssh_fix12.tar
http://aix.software.ibm.com/aix/efixes/security/openssh_fix12.tar
https://aix.software.ibm.com/aix/efixes/security/openssh_fix12.tar

The links above are to a tar file containing this signed advisory, interim fixes, and OpenSSL signatures for each interim fix. These fixes below include prerequisite checking. This will enforce the correct mapping between the fixes and AIX releases.

Note that the tar file contains Interim fixes that are based on OpenSSH version as given below.

You must be on the ‘prereq for installation’ level before applying the interim fix. This may require installing a new level (prereq version) first.

AIX Level Interim Fix (*.Z) Fileset Name (prereq for installation) KEY
---------------------------------------------------------------------------------------------
5.3, 6.1, 7.1, 7.2 15473_fix.180919.epkg.Z openssh.base (7.5.102.1500 version) key_w_fix

VIOS Level Interim Fix (*.Z) Fileset Name (prereq for installation) KEY
---------------------------------------------------------------------------------------------
2.2.x 15473_fix.180919.epkg.Z openssh.base (7.5.102.1500 version) key_w_fix

Latest level of OpenSSH fileset is available from the web download site:
https://www14.software.ibm.com/webapp/iwm/web/reg/download.do?source=aixbp&amp;lang=en_US&amp;S_PKG=openssh&amp;cp=UTF-8

To extract the fix from the tar file:

tar xvf openssh_fix12.tar
cd openssh_fix12

Verify you have retrieved the fix intact:

The checksums below were generated using the “openssl dgst -sha256 file” command is the following:

openssl dgst -sha256 filename KEY
-----------------------------------------------------------------------------------------------------
45ac81fc8766c41a7244ec2481ffa38aa90ca1b7c99b0b0acb1e4d82826b842a 15473_fix.180919.epkg.Z key_w_csum

Published advisory OpenSSH signature file location:

http://aix.software.ibm.com/aix/efixes/security/openssh_advisory12.asc.sig
https://aix.software.ibm.com/aix/efixes/security/openssh_advisory12.asc.sig
ftp://aix.software.ibm.com/aix/efixes/security/openssh_advisory12.asc.sig

openssl dgst -sha1 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file]

openssl dgst -sha1 -verify [pubkey_file] -signature [ifix_file].sig [ifix_file]

B. FIX AND INTERIM FIX INSTALLATION

After applying fix, IBM recommends that you regenerate your SSH keys as a precaution.

IMPORTANT: If possible, it is recommended that a mksysb backup of the system be created. Verify it is both bootable and readable before proceeding.

To preview a fix installation:

installp -a -d fix_name -p all # where fix_name is the name of the

fix package being previewed.

To install a fix package:

installp -a -d fix_name -X all # where fix_name is the name of the

fix package being installed.

Interim fixes have had limited functional and regression testing but not the full regression testing that takes place for Service Packs; however, IBM does fully support them.

Interim fix management documentation can be found at:

http://www14.software.ibm.com/webapp/set2/sas/f/aix.efixmgmt/home.html

To preview an interim fix installation:

emgr -e ipkg_name -p # where ipkg_name is the name of the

interim fix package being previewed.

To install an interim fix package:

emgr -e ipkg_name -X # where ipkg_name is the name of the

interim fix package being installed.

Workarounds and Mitigations

None.