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Home » Hacking News » NetBSD Security Advisories

NetBSD Security Advisories

by phiber on May 31st, 2001 We bring you three NetBSD Security Advisories. This article contains the following advisories: Denial of service using bogus fragmented IPv4 packets (2001-006), Processes can gain "Supervisor" privileges on sh3 (2001-008) and IP Filter may incorrectly pass packets (2001-007).
"Read More" for more information and downloads.


NetBSD Security Advisory 2001-006

Malicious parties may be able to prevent a NetBSD node from communicating with other nodes by transmitting a lot of bogus fragmented IPv4 packets.

For the attack to be effective, the attacker needs to have good network connectivity to the victim node (like logged onto the victim machine itself, connected by a fat LAN, or whatever).

There are exploits for this problem available on the Internet.

However, the attack is timing dependent and the attack is not always successful.

- Workaround

(1) Upgrade the system from newer sources or binaries:



Compile and install a kernel which has the sysctl(3) variable net.inet.ip.maxfragpackets in the sysctl MIB. With this variable, you can limit the number of IPv4 fragment reassembly queues kept on the system. The value needs to be picked carefully, considering the role of the node (i.e. if the node is a busy web server, you may want to set the value
higher). Note that, however, even with the configuration knob, it is possible for attackers to transmit a lot of bogus IPv4 fragmented packets, and prevent other fragmented IPv4 traffic from getting reassembled. Unfragmented IPv4 communication will be kept safe by the variable.



Systems running NetBSD-current dated from before April 17, 2001 should be upgraded to NetBSD-current dated April 17, 2001 or later.



Systems running NetBSD 1.5.x systems dated from before April 24, 2001 should be upgraded to NetBSD 1.5.x dated April 24, 2001 or later.

NetBSD 1.5.1 will ship with the fix.



There is no fix to 1.4.x available at this time.



(2) Increase the kernel option NMBCLUSTERS



Use an appropriate value for NMBCLUSTERS for the node.

Normally, it is the cluster mbufs which go into a starvation state with this attack. By setting NMBCLUSTERS to a higher value, you may be able to prevent the mbuf memory pool from starving.



Note that a couple of NetBSD device drivers pre-allocate cluster mbufs within the driver, for performance reasons and DMA management reasons. For example, the fxp driver pre-allocates 64 cluster mbufs per interface. If you are using such network cards, you will want to raise NMBCLUSTERS even more.

Download



----

NetBSD Security Advisory 2001-007

IP Filter (ipf) - the IP packet filtering software in NetBSD - has a
bug where the checks on a fragmented packet are incomplete and
it may be possible to abuse this to bypass filter rules.
Fragmented packets may be stored in a ``fragment cache'' in certain
circumstances. The fragment cache is checked for a packet match
before any of the filter rules are checked. There were insufficient
checks made on fragmented packets before inserting the packet into
the fragment cache.

This problem is most likely to occur if "keep frags" or "keep state"
is used in the ipf rules, but it is possible if the ftp NAT proxy
is used in the ipnat rules.



- Workaround

Upgrade the system from newer sources or binaries.



Systems running NetBSD-current dated from before April 6, 2001
should be upgraded to NetBSD-current dated April 6, 2001 or later.



Systems running NetBSD 1.5.x systems dated from before April 14, 2001
should be upgraded to NetBSD 1.5.x dated April 14, 2001 or later.
NetBSD 1.5.1 will ship with the fix.



Systems running NetBSD 1.4.x systems dated from before April 14, 2001
should be upgraded to NetBSD 1.4.x dated April 14, 2001 or later.

Download the whole advisory.



----

NetBSD Security Advisory 2001-008

Missing validation of user-supplied arguments to a system call can
allow user applications on the sh3 platform to execute code with
supervisor privileges, bypassing normal system protections.



This problem is only present on the sh3 platform, which includes the
dreamcast, evbsh3, hpcsh and mmeye ports.

- Workaround

Systems running NetBSD/evbsh3, NetBSD/dreamcast, NetBSD/hpcsh or
NetBSD/mmeye are vulnerable. Although the NetBSD Project has not
distributed binary releases for these ports yet, binary snapshots
of development versions are known to be in use.



Systems running NetBSD-current dated from before May 16, 2001 should
be upgraded to NetBSD-current dated May 16, 2001 or later.



Systems running NetBSD-release-1-5 dated from before May 27, 2001
should be upgraded to NetBSD-release-1-5 dated May 27, 2001 or later.

Download the whole advisory.


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