Security Bulletin
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 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&lang=en_US&S_PKG=openssh&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.
Get Notified about Future Security Bulletins
References
Acknowledgement
None.
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
Review the IBM security bulletin disclaimer and definitions regarding your responsibilities for assessing potential impact of security vulnerabilities to your environment.
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Document Information
Modified date:
24 October 2018
UID
ibm10733751