Security Bulletin: Vulnerability in MIT Kerberos 5 affects PowerSC (CVE-2021-37750)

Summary

There is a vulnerability in MIT Kerberos 5 that affects PowerSC (CVE-2021-37750).

Vulnerability Details

CVEID:CVE-2021-37750
**DESCRIPTION:**MIT Kerberos 5 (aka krb5) is vulnerable to a denial of service, caused by a NULL pointer dereference flaw in kdc/do_tgs_req.c in the Key Distribution Center (KDC). By sending a specially-crafted FAST TGS request with no server field, a remote authenticated attacker could exploit this vulnerability to cause a denial of service condition.
CVSS Base score: 6.5
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/208020 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)

Affected Products and Versions

The vulnerabilities in the following filesets are being addressed:

Note: To find out whether the affected PowerSC filesets are installed on your systems, refer to the lslpp command found in AIX user’s guide. To find out whether the affected krb5 filesets are installed on your systems, refer to the rpm command found in AIX user’s guide.

Example: lslpp -l | grep powerscStd

Example: rpm -qa | grep krb5

Remediation/Fixes

A. FIXES

Fixes are available.

The fixes can be downloaded via ftp or http from:

ftp://aix.software.ibm.com/aix/efixes/powersc/security/krb5_fix.tar

<http://aix.software.ibm.com/aix/efixes/powersc/security/krb5_fix.tar&gt;

<https://aix.software.ibm.com/aix/efixes/powersc/security/krb5_fix.tar&gt;

The link above is to a tar file containing this signed advisory, open source fix packages, and OpenSSL signatures for each package.

To extract the fixes from the tar file:

tar xvf krb5_fix.tar

cd krb5_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.

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/powersc/security/krb5_advisory.asc.sig&gt;

<https://aix.software.ibm.com/aix/efixes/powersc/security/krb5_advisory.asc.sig&gt;

ftp://aix.software.ibm.com/aix/efixes/powersc/security/krb5_advisory.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 extract the fixes from the tar file:

tar xvf krb5_fix.tar

cd krb5_fix

To install a fix package:

rpm -ivh *.rpm

rpm -Uvh *.rpm

To install any dependencies along with the fix package:

yum update krb5-libs

Workarounds and Mitigations

None