SSRT5954 rev.0 - HP-UX TCP/IP Remote Denial of Service (DoS)
From: Security Alert (secure_at_hpchs.cup.hp.com)
Date: Mon, 25 Apr 2005 18:59:24 GMT
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HP SECURITY BULLETIN
HPSBUX01137 REVISION: 0
SSRT5954 rev.0 - HP-UX TCP/IP Remote Denial of Service (DoS)
There are no restrictions for distribution of this Security
Bulletin provided that it remains complete and intact.
The information in this Security Bulletin should be acted upon
as soon as possible.
24 April 2005
POTENTIAL SECURITY IMPACT:
Remote Denial of Service (DoS)
HP Software Security Response Team
A potential security vulnerability has been identified with HP-UX
running TCP/IP (IPv4). This vulnerability could be remotely
exploited by an unauthorized user to cause a Denial of Service
SUPPORTED SOFTWARE VERSIONS*: ONLY impacted versions are listed.
HP-UX B.11.00, B.11.04, B.11.11, B.11.22, B.11.23
running TCP/IP (IPv4).
action: set ip_pmtu_strategy = 0 or 3
END AFFECTED VERSIONS
Certain network traffic can result in a Denial of Service (DoS)
for HP-UX systems running TCP/IP (IPv4). Receiving a certain
packet on any open TCP/IP connection can result in a Denial of
Service (DoS) condition which can only be corrected by a reboot of
the affected system.
Until patches are available to resolve the issue the Denial of
Service (DoS) can be avoided by setting the ip_pmtu_strategy
parameter to either 0 or 3.
Discussion of ip_pmtu_strategy
The default value for ip_pmtu_strategy is 1. This allows for PMTU
discovery. Once the issue of this Security Bulletin has been
resolved via patches the ip_pmtu_strategy value of 1 will again be
the preferred setting for most situations.
The ip_pmtu_strategy values of 0 and 3 set the PMTU to a fixed
size for destinations which are not on the local network.
The ip_pmtu_strategy value of 0 sets the PMTU to 576 bytes.
Routers are required to handle packets of at least this size.
The ip_pmtu_strategy value of 3 sets the PMTU to 1500 bytes. This
will generally result in more efficient transmission than the 576
byte PMTU. If it is known that the routers involved can handle a
1500 byte MTU the ip_pmtu_strategy value of 3 is preferred.
Patch requirements for setting ip_pmtu_strategy to 3
All affected HP-UX versions allow setting ip_pmtu_strategy to 0.
B.11.22 and B.11.23 have no patch requirements for
setting ip_pmtu_strategy to 3.
B.11.11, B.11.04, and B.11.00 require the following patches in
order to set ip_pmtu_strategy to 3:
B.11.11 - PHNE_25642 or subsequent
B.11.04 - PHNE_26101 or subsequent
B.11.00 - PHNE_25423 or subsequent
Reboot requirement for setting ip_pmtu_strategy
The ip_pmtu_strategy parameter can be set via the ndd(1M) command
or by changing the nddconf file and rebooting the system. The
ndd(1M) command only affects new connections. Existing
connections will remain vulnerable until they terminate or until
the system is rebooted and the nddconf value of ip_pmtu_strategy
It has been recommended in several places including HP-UX
Bastille, System Health Check, and the Security Bulletin
HPSBUX0001-110 that ip_pmtu_strategy be set to 1. This
recommendation was made to avoid issues with which
occurred when ip_pmtu_strategy was set to 2. The value 1
was recommended because it is the system default and
for most situations results in the best performance. However,
the values 0 and 3 also avoid the issues which occurred when
ip_pmtu_strategy was set to 2. As mentioned above once the
issue of this Security Bulletin has been resolved via patches the
ip_pmtu_strategy setting of 1 will again be the preferred setting
for most situations.
There is a defect that will cause "ndd -c" to fail if there are
more than 10 directives in /etc/rc.config.d/nddconf. That defect
is fixed in the following patches:
B.11.11 - PHNE_25644 or subsequent
B.11.04 - PHNE_26076 or subsequent
B.11.00 - PHNE_26125 or subsequent
Until patches are available the Denial of Service (DoS) can be
avoided by setting the ip_pmtu_strategy parameter to 0 or 3.
If the ip_pmtu_strategy value of 3 is desired for B.11.11, B11.04,
or B.11.00 apply the patches listed in the Background section.
Edit /etc/rc.config.d/nddconf to add the following:
where 'n' is the next available index value as described in the
As discussed in the Background section the system must be rebooted
for the new ip_pmtu_strategy to take effect.
Until the system can be rebooted the ip_pmtu_strategy value for
new connections can be set with the ndd(1M) command:
/usr/bin/ndd -set /dev/ip ip_pmtu_strategy 0
/usr/bin/ndd -set /dev/ip ip_pmtu_strategy 3
MANUAL ACTIONS: Yes - NonUpdate
set ip_pmtu_strategy = 0 or 3
BULLETIN REVISION HISTORY:
Revision 0: 24 April 2005
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