I regret to inform you about multiple new releases of the Net-SNMP
suite. There is a ***CRITICAL SECURITY ISSUE*** that appears in the
SNMPv3 implementation that exists in every release made since the
SNMPv3 code was written (which includes all versions of UCD-SNMP and
Net-SNMP beyond version 4.0). Please read the following summary that
explains how this might impact you and what mitigation you can take:



Let me upgrade NOW! Where's the code?
----------------------------------------
Grab one of the new releases from our sourceforge download sites:

http://www.net-snmp.org/download.html



Are there vulnerability tracking numbers?
----------------------------------------
Yes:

CERT: VU#878044
CVE: CVE-2008-0960



What does it affect?
----------------------------------------
The issue is part of the code that checks the authentication field of
the SNMPv3 packet. A carefully crafted SNMPv3 packet may succeed in
getting passed the authentication check when it should not. It does
not affect authorization checks (which is done by the VACM system) so
even if the falsified authentication succeeds, an attacker would only be
granted access to the portions of the SNMP MIB space that the account
would have been normally granted access to.



What about SNMPv1 and SNMPv2c?
----------------------------------------
This does not affect SNMPv1 nor SNMPv2c. SNMPv1 and SNMPv2c are less
secure than SNMPv3 even when considering this problem.



What should I do?
----------------------------------------
1) Install one of the updated packages immediately which will fix the
problems. If you do that, you need not take any of the other steps
below.

If you are using Net-SNMP through a third party distribution such
as your operating system vendor they should be release updates for
their systems ASAP as well (likely today for most of them).



2) If this is impossible to do quickly and immediately you can do any
of the following to help:

a) Put firewalls in front of your SNMP ports. This is generally
recommended anyway, since allowing external access to any server
that doesn't need to be accessible across the entire Internet
is always good practice.

b) Utilize encryption in addition to authentication. Turning on
*and requiring* DES or AES support for your SNMPv3 users will at
least make attacking a system more difficult. Cryptographically
speaking, encryption is not a good form of authentication but in
this case it will be better than not using it even if you don't
need to protect your SNMPv3 packets from disclosure. Make sure
you change your VACM authorization settings to require that
encryption be used. For example, in the rwuser or rouser config
tokens add "priv" to the end. For example:

Change from:
rwuser wes
rouser joe

Change to:
rwuser wes priv
rouser joe priv

c) Decrease what an authenticated packet can do. If you do not
need SNMP SETs to be supported on your network, you con turn
them off by disallowing them. For example:

Change from:
rwuser wes priv

Change to:
rouser wes priv
^

d) Detect illegal authentication attempts by turn on authentication
notifications. If you are using SNMP notifications (traps and
informs) in your network of SNMP agents, adding the following
line to your snmpd.conf file will make the agent send a trap or
inform when someone fails to authenticate properly to the
agent. Because an attacker trying to exploit this issue will
not succeed every time you should get notifications that devices
are being targeted:

authtrapenable 1

(You will also need to define trap destinations if you have not already)



Is there a patch instead?
----------------------------------------

Yes, a direct small patch is available from:

https://sourceforge.net/tracker/inde...94&atid=456380

--
Wes Hardaker
Sparta, Inc.

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