Summary

A vulnerability in ISC BIND could allow a remote attacker to poison the cache (CVE-2021-25220). AIX uses ISC BIND as part of its DNS functions.

Vulnerability Details

CVEID:CVE-2021-25220
**DESCRIPTION:**ISC BIND could allow a remote attacker to bypass security restrictions, caused by an error when using DNS forwarders. An attacker could exploit this vulnerability to poison the cache with incorrect records leading to queries being made to the wrong servers, which might also result in false information being returned to clients.
CVSS Base score: 6.8
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/221991 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:N)

Affected Products and Versions

The following fileset levels are vulnerable:

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.server

Remediation/Fixes

A. APARS

IBM has assigned the following APARs to this problem:

Subscribe to the APARs here:

<https://www.ibm.com/support/pages/apar/IJ40614&gt;

<https://www.ibm.com/support/pages/apar/IJ40615&gt;

<https://www.ibm.com/support/pages/apar/IJ40616&gt;

<https://www.ibm.com/support/pages/apar/IJ40617&gt;

<https://www.ibm.com/support/pages/apar/IJ40674&gt;

<https://www.ibm.com/support/pages/apar/IJ41139&gt;

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

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/bind_fix21.tar

<http://aix.software.ibm.com/aix/efixes/security/bind_fix21.tar&gt;

<https://aix.software.ibm.com/aix/efixes/security/bind_fix21.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.

Please note that the above table refers to AIX TL/SP level as opposed to fileset level, i.e., 7.2.5.2 is AIX 7200-05-02.

Please reference the Affected Products and Version section above for help with checking installed fileset levels.

The above fixes are cumulative and address previously issued AIX/VIOS BIND security bulletins.

To extract the fixes from the tar file:

tar xvf bind_fix21.tar

cd bind_fix21

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/bind_advisory21.asc.sig&gt;

<https://aix.software.ibm.com/aix/efixes/security/bind_advisory21.asc.sig&gt;

ftp://aix.software.ibm.com/aix/efixes/security/bind_advisory21.asc.sig

C. 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