Summary

A vulnerability in zlib and zlibNX could allow a remote attacker to cause a denial of service (CVE-2018-25032). AIX uses zlib and zlibNX as part of its data compression functions.

Vulnerability Details

CVEID:CVE-2018-25032
**DESCRIPTION:**Zlib is vulnerable to a denial of service, caused by a memory corruption in the deflate operation. By using many distant matches, a remote attacker could exploit this vulnerability to cause the application to crash.
CVSS Base score: 7.5
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/222615 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

The following fileset levels are vulnerable:

For zlib:

For zlibNX:

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 zlibNX.rte

Remediation/Fixes

A. FIXES

IBM strongly recommends addressing the vulnerability now.

AIX and VIOS fixes are available.

The AIX and VIOS fixes can be downloaded via ftp or http from:

ftp://aix.software.ibm.com/aix/efixes/security/zlib_fix.tar

<http://aix.software.ibm.com/aix/efixes/security/zlib_fix.tar&gt;

<https://aix.software.ibm.com/aix/efixes/security/zlib_fix.tar&gt;

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.

For zlib:

For zlibNX:

To extract the fixes from the tar file:

tar xvf zlib_fix.tar

cd zlib_fix

Verify you have retrieved the fixes intact:

The checksums below were generated using the “openssl dgst -sha256 [filename]” command as the following:

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 Support at <http://ibm.com/support/&gt; and describe the discrepancy.

openssl dgst -sha256 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file]

openssl dgst -sha256 -verify [pubkey_file] -signature [ifix_file].sig [ifix_file]

Published advisory OpenSSL signature file location:

<http://aix.software.ibm.com/aix/efixes/security/zlib_advisory.asc.sig&gt;

<https://aix.software.ibm.com/aix/efixes/security/zlib_advisory.asc.sig&gt;

ftp://aix.software.ibm.com/aix/efixes/security/zlib_advisory.asc.sig

B. FIX AND INTERIM FIX INSTALLATION

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&gt;

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