Vulnerability in MD5 Signature and Hash Algorithm affects OpenSSL on AIX

IBM SECURITY ADVISORY

First Issued: Fri Jan 29 15:43:20 CST 2016

The most recent version of this document is available here:

http://aix.software.ibm.com/aix/efixes/security/openssl_advisory16.asc
https://aix.software.ibm.com/aix/efixes/security/openssl_advisory16.asc
ftp://aix.software.ibm.com/aix/efixes/security/openssl_advisory16.asc

Security Bulletin: Vulnerability in MD5 Signature and Hash Algorithm affects
OpenSSL on AIX (CVE-2015-7575)

===============================================================================

SUMMARY:

The MD5 �SLOTH� vulnerability on TLS 1.2 affects OpenSSL on AIX.

===============================================================================

VULNERABILITY DETAILS:

CVEID: CVE-2015-7575
DESCRIPTION: The TLS protocol could allow weaker than expected security 
    caused by a collision attack when using the MD5 hash function for 
    signing a ServerKeyExchange message during a TLS handshake. An attacker
    could exploit this vulnerability using man-in-the-middle techniques to
    impersonate a TLS server and obtain credentials.
CVSS Base Score: 7.1
CVSS Temporal Score: See 
    https://exchange.xforce.ibmcloud.com/vulnerabilities/109415 for the 
    current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/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 
    --------------------------------------------------
    openssl.base     1.0.1.500    1.0.1.515   key_w_fs


    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 openssl.base

REMEDIATION:

    A. FIXES

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

        ftp://aix.software.ibm.com/aix/efixes/security/openssl_fix16.tar
        http://aix.software.ibm.com/aix/efixes/security/openssl_fix16.tar
        https://aix.software.ibm.com/aix/efixes/security/openssl_fix16.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.
        
        Note that the tar file contains Interim fixes that are based on 
        OpenSSL version.

        AIX Level           Interim Fix (*.Z)        Fileset Name(prereq for installation) KEY
        --------------------------------------------------------------------------------------------
        5.3, 6.1, 7.1, 7.2  101a_fix.160129.epkg.Z   openssl.base(1.0.1.515 version)       key_w_fix

        VIOS Level     Interim Fix (*.Z)             Fileset Name(prereq for installation) KEY
        --------------------------------------------------------------------------------------------
        2.2.*          101a_fix.160129.epkg.Z        openssl.base(1.0.1.515 version)       key_w_fix


        You should verify applying this fix does not cause any 
        compatibility issues. The fix disables MD5 signature hash by 
        default. 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 MD5 signature hash and take
        appropriate mitigation and remediation actions.
        
        To extract the fixes from the tar file:

        tar xvf openssl_fix16.tar
        cd openssl_fix16

        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
        ----------------------------------------------------------------------------------------------------
        bfc26950a361720c2a3692e7dd7f5ae13f782f419b634c34fc42add5b4e83724  101a_fix.160129.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
        [email protected] 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/openssl_advisory16.asc.sig
        https://aix.software.ibm.com/aix/efixes/security/openssl_advisory16.asc.sig
        ftp://aix.software.ibm.com/aix/efixes/security/openssl_advisory16.asc.sig 

    B. 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.


WORKAROUNDS AND MITIGATIONS:

    None.

===============================================================================

CONTACT US:

Note: Keywords labeled as KEY in this document are used for parsing
purposes.

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Comments regarding the content of this announcement can be
directed to:

    [email protected]

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 [email protected] 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 v3 Guide:  http://www.first.org/cvss/user-guide
On-line Calculator v3:
    http://www.first.org/cvss/calculator/3.0

ACKNOWLEDGEMENTS:

Reported to IBM by Karthikeyan Bhargavan at INRIA in Paris, France.

CHANGE HISTORY:

First Issued: Fri Jan 29 15:43:20 CST 2016

===============================================================================

*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.