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AUSCERT External Security Bulletin Redistribution
ESB-2015.2054
Security Bulletin: Vulnerability in Diffie-Hellman ciphers
affects sendmail on AIX (CVE-2015-4000)
10 August 2015
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: sendmail
Publisher: IBM
Operating System: AIX
Impact/Access: Access Privileged Data -- Remote/Unauthenticated
Provide Misleading Information -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2015-4000
Reference: ASB-2015.0070
ASB-2015.0066
ESB-2015.2040
ESB-2015.2038
ESB-2015.2033
ESB-2015.2027
ESB-2015.2022
ESB-2015.2018
Original Bulletin:
http://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc
- --------------------------BEGIN INCLUDED TEXT--------------------
IBM SECURITY ADVISORY
First Issued: Fri Aug 7 15:15:59 CDT 2015
The most recent version of this document is available here:
http://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc
https://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc
ftp://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc
Security Bulletin: Vulnerability in Diffie-Hellman ciphers affects
sendmail on AIX (CVE-2015-4000)
===============================================================================
SUMMARY:
The Logjam Attack on TLS connections using the Diffie-Hellman (DH) key
exchange protocol affects sendmail when using the sendmail_ssl binary on
AIX.
===============================================================================
VULNERABILITY DETAILS:
CVEID: CVE-2015-4000
DESCRIPTION: The TLS protocol could allow a remote attacker to obtain
sensitive information, caused by the failure to properly convey a
DHE_EXPORT ciphersuite choice. An attacker could exploit this
vulnerability using man-in-the-middle techniques to force a downgrade
to 512-bit export-grade cipher. Successful exploitation could allow
an attacker to recover the session key as well as modify the contents
of the traffic. This vulnerability is commonly referred to as
"Logjam".
CVSS Base Score: 4.3
CVSS Temporal Score: See
https://exchange.xforce.ibmcloud.com/vulnerabilities/103294 for the
current score
CVSS Environmental Score*: Undefined
CVSS Vector: (AV:N/AC:M/Au:N/C:P/I:N/A:N)
AFFECTED PRODUCTS AND VERSIONS:
AIX 5.3, 6.1, 7.1
VIOS 2.2.x
The following AIX fileset levels are vulnerable:
AIX Fileset Lower Level Upper Level KEY
--------------------------------------------------------
bos.net.tcp.client 6.1.0.0 6.1.8.19 key_w_fs
bos.net.tcp.client 6.1.0.0 6.1.9.45 key_w_fs
bos.net.tcp.client 7.1.0.0 7.1.2.19 key_w_fs
bos.net.tcp.client 7.1.0.0 7.1.3.45 key_w_fs
AIX Fileset (VIOS) Lower Level Upper Level
------------------------------------------------------------
bos.net.tcp.client 6.1.0.0(2.2.0.0) 6.1.8.19(2.2.2.6)
bos.net.tcp.client 6.1.0.0(2.2.0.0) 6.1.9.45(2.2.3.50)
Note: to find out whether the affected filesets are installed
on your systems, refer to the lslpp command found in AIX user's guide.
Example: lslpp -L | grep -i bos.net.tcp.client
REMEDIATION:
A. APARS
IBM has assigned the following APARs to this problem:
Please note that these only apply to the SSL-enabled
sendmail binary, /usr/sbin/sendmail_ssl. The default
sendmail bindary, /usr/sbin/sendmail, is not vulnerable
to the Logjam attack.
AIX Level APAR Availability SP KEY
---------------------------------------------------
6.1.9 IV75643 12/04/15 SP6 key_w_apar
7.1.3 IV75646 2/26/16 SP6 key_w_apar
Subscribe to the APARs here:
http://www.ibm.com/support/docview.wss?uid=isg1IV75643
http://www.ibm.com/support/docview.wss?uid=isg1IV75646
By subscribing, you will receive periodic email alerting you
to the status of the APAR, and a link to download the fix once
it becomes available.
B. FIXES
Fixes are available. Please note that the sendmail_ssl fixes
require a current version of OpenSSL that includes the Logjam
fix. Please see the previously published OpenSSL bulletin:
http://aix.software.ibm.com/aix/efixes/security/openssl_advisory14.asc
https://aix.software.ibm.com/aix/efixes/security/openssl_advisory14.asc
ftp://aix.software.ibm.com/aix/efixes/security/openssl_advisory14.asc
The sendmail_ssl fixes can be downloaded via ftp or http from:
ftp://aix.software.ibm.com/aix/efixes/security/sendmail_fix.tar
http://aix.software.ibm.com/aix/efixes/security/sendmail_fix.tar
https://aix.software.ibm.com/aix/efixes/security/sendmail_fix.tar
The link above is to a tar file containing this signed
advisory, fix packages, and OpenSSL signatures for each package.
The fixes below include prerequisite checking. This will
enforce the correct mapping between the fixes and AIX
Technology Levels.
Please note that these only apply to the SSL-enabled
sendmail binary, /usr/sbin/sendmail_ssl. The default
sendmail bindary, /usr/sbin/sendmail, is not vulnerable
to the Logjam attack.
AIX Level Interim Fix (*.Z) KEY
------------------------------------------------
6.1.8.6 IV75644m6a.150731.epkg.Z key_w_fix
6.1.9.5 IV75643m5a.150731.epkg.Z key_w_fix
7.1.2.6 IV75645m6a.150731.epkg.Z key_w_fix
7.1.3.5 IV75646m5a.150731.epkg.Z key_w_fix
To extract the fixes from the tar file:
tar xvf sendmail_fix.tar
cd sendmail_fix
Verify you have retrieved the fixes intact:
The checksums below were generated using the
"openssl dgst -sha256 file" command as the followng:
openssl dgst -sha256 filename KEY
-----------------------------------------------------------------------------------------------------
517637a4871e869ea9322d8c91c94ef8c74ee17821fbdf85f84e52dfd99233f8 IV75644m6a.150731.epkg.Z key_w_csum
af34ca8e20e0440a35dd4fd8caaa051b892f4d30f7cb7fa3f179efcd7f7ab834 IV75643m5a.150731.epkg.Z key_w_csum
e8916a64220b50eb24df48276fb2a8ddbf50e7c42286eee52841aa7e14864c7c IV75645m6a.150731.epkg.Z key_w_csum
ea4f46484d3934fdfdf73293f0ca47abcb38f930e8e5f619fa2af720e390dc4d IV75646m5a.150731.epkg.Z key_w_csum
These sums should match exactly. The OpenSSL signatures in the tar
file and on this advisory can also be used to verify the
integrity of the fixes. If the sums or signatures cannot be
confirmed, contact IBM AIX Security at
security-alert@austin.ibm.com and describe the discrepancy.
openssl dgst -sha1 -verify <pubkey_file> -signature <advisory_file>.sig <advisory_file>
openssl dgst -sha1 -verify <pubkey_file> -signature <ifix_file>.sig <ifix_file>
Published advisory OpenSSL signature file location:
http://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc.sig
https://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc.sig
ftp://aix.software.ibm.com/aix/efixes/security/sendmail_advisory.asc.sig
C. FIX AND INTERIM FIX INSTALLATION
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.
You should verify applying this configuration change does not cause
any compatibility issues. If you change the default setting after
applying the fix, you will expose yourself to the attack described
above. IBM recommends that you review your entire environment to
identify other areas where you have enabled the Diffie-Hellman
key-exchange protocol used in TLS and take appropriate mitigation and
remediation actions.
WORKAROUNDS AND MITIGATIONS:
None.
===============================================================================
CONTACT US:
If you would like to receive AIX Security Advisories via email,
please visit "My Notifications":
http://www.ibm.com/support/mynotifications
To view previously issued advisories, please visit:
http://www14.software.ibm.com/webapp/set2/subscriptions/onvdq
Comments regarding the content of this announcement can be
directed to:
security-alert@austin.ibm.com
To obtain the OpenSSL public key that can be used to verify the
signed advisories and ifixes:
Download the key from our web page:
http://www.ibm.com/systems/resources/systems_p_os_aix_security_pubkey.txt
To obtain the PGP public key that can be used to communicate
securely with the AIX Security Team via security-alert@austin.ibm.com you
can either:
A. Download the key from our web page:
http://www.ibm.com/systems/resources/systems_p_os_aix_security_pgppubkey.txt
B. Download the key from a PGP Public Key Server. The key ID is:
0x28BFAA12
Please contact your local IBM AIX support center for any
assistance.
REFERENCES:
Complete CVSS Guide: http://www.first.org/cvss/cvss-guide.html
On-line Calculator V2:
http://nvd.nist.gov/cvss.cfm?calculator&adv&version=2
ACKNOWLEDGEMENTS:
CVE-2015-4000 was reported to IBM by The WeakDH team at https://weakdh.org
CHANGE HISTORY:
First Issued: Fri Aug 7 15:15:59 CDT 2015
===============================================================================
*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
According to the Forum of Incident Response and Security Teams (FIRST), the
Common Vulnerability Scoring System (CVSS) is an "industry open standard
designed to convey vulnerability severity and help to determine urgency and
priority of response." IBM PROVIDES THE CVSS SCORES "AS IS" WITHOUT WARRANTY
OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT
OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY.
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