Security Bulletin: Vulnerabilities in OpenSSH affect AIX (CVE-2018-20685 CVE-2018-6109 CVE-2018-6110 CVE-2018-6111)

Summary

Vulnerabilities in OpenSSH affect AIX.

Vulnerability Details

CVEID: CVE-2019-6109 DESCRIPTION: OpenSSH could allow a remote attacker to conduct spoofing attacks, caused by missing character encoding in the progress display. A man-in-the-middle attacker could exploit this vulnerability to spoof scp client output.
CVSS Base Score: 3.1
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/155488&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N)

CVEID: CVE-2019-6110 DESCRIPTION: OpenSSH could allow a remote attacker to conduct spoofing attacks, caused by accepting and displaying arbitrary stderr output from the scp server. A man-in-the-middle attacker could exploit this vulnerability to spoof scp client output.
CVSS Base Score: 3.1
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/155487&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N)

CVEID: CVE-2019-6111 DESCRIPTION: OpenSSH could allow a remote attacker to overwrite arbitrary files on the system, caused by missing received object name validation by the scp client. The scp implementation accepts arbitrary files sent by the server and a man-in-the-middle attacker could exploit this vulnerability to overwrite unrelated files.
CVSS Base Score: 5.3
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/155486&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N)

CVEID: CVE-2018-20685 DESCRIPTION: OpenSSH could allow a remote attacker to bypass security restrictions, caused by directory name validation by scp.c in the scp client. A man-in-the-middle attacker could exploit this vulnerability using the filename of . or an empty filename to bypass access restrictions and modify permissions of the target directory.
CVSS Base Score: 7.5
CVSS Temporal Score: See <https://exchange.xforce.ibmcloud.com/vulnerabilities/155484&gt; for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H)

Affected Products and Versions

The following fileset levels are vulnerable:

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

FIXES

A fix is available for CVE-2018-20685, CVE-2019-6109, and CVE-2019-6111.

Please see the WORKAROUNDS AND MITIGATIONS section for mitigation steps in response to CVE-2019-6110.

To extract the fixes from the tar file:

zcat openssh-7.5.102.1800.tar.Z | tar xvf

Please refer to the Readme file to be aware of the changes that are part of the release.

IMPORTANT: If possible, it is recommended that a mksysb backup of the system be created. Verify it is both bootable and readable before proceeding. Note that all the previously reported security vulnerability fixes are also included in above mentioned fileset level. Please refer to the readme file (provided along with the fileset) for the complete list of vulnerabilities fixed.

To preview the fix installation:

installp -apYd . openssh

To install the fix package:

installp -aXYd . openssh

Published advisory OpenSSH signature file location:

http://aix.software.ibm.com/aix/efixes/security/openssh_advisory13.asc.sig
https://aix.software.ibm.com/aix/efixes/security/openssh_advisory13.asc.sig
ftp://aix.software.ibm.com/aix/efixes/security/openssh_advisory13.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]

Workarounds and Mitigations

The potential impact of CVE-2019-6110 may be mitigated by using the sftp command in place of the scp command.