SSRT5954 rev.5 - HP-UX TCP/IP Remote Denial of Service (DoS)
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HP SECURITY BULLETIN
HPSBUX01137 REVISION: 5
SSRT5954 rev.5 - 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 July 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.11.11, B.11.22, B.11.23.
Note: To determine if a system has an affected version,
search the output of "swlist -a revision -l fileset"
for an affected fileset. Then determine if the
recommended patch or update is installed.
->action: install PHNE_33159
->action: install preliminary binary files per HPSBUX01164
->action: install PHNE_32606
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. The Denial of Service (DoS) is characterized
by high cpu utilization and a lack of response on any I/O port
including the system console.
Until patches are available to resolve the issue the Denial of
ervice (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.
->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.
->Note: For IPv4 the Next-Hop MTU may be as low as 68 bytes.
-> Therefore setting ip_pmtu_strategy=0 or 3 may cause
-> connections to stall.
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 requires PHNE_25642 or subsequent in order to set
ip_pmtu_strategy to 3.
Reboot requirement for setting ip_pmtu_strategy
Any existing connection presents the potential for a Denial of
Service (DoS). Because of this it is recommended that the
/etc/rc.config.d/nddconf be modified as discussed below and the
system be rebooted.
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 patch:
B.11.11 - PHNE_25644 or subsequent
->Patches are available for the core TCP/IP product for B.11.11
-> and B.11.23 from < http://itrc.hp.com>:
-> For B.11.11 - PHNE_33159 or subsequent
-> For B.11.23 - PHNE_32606 or subsequent
-> Binary files are available for B.11.22 as discussed in
->Until patches are available for the IPSec product for B.11.11
->and B.11.23 the issue can be avoided by setting
->ip_pmtu_strategy parameter to 0 or 3.
->Procedure to set ip_pmtu_strategy for B.11.22 or the IPSec
->product on B.11.11 and B.11.23
Edit /etc/rc.config.d/nddconf to add the following:
where 'n' is the next available index value as described in the
This value will take effect when the system is rebooted.
Until the system can be rebooted use the following command
to read the /etc/rc.config.d/nddconf file and set the tunable
The ip_pmtu_strategy parameter can be displayed by the following
/usr/bin/ndd -get /dev/ip ip_pmtu_strategy
Note: Since open connections will remain potentially vulnerable
until they are closed and certain internal data structures
are released it is recommended that the system be rebooted.
MANUAL ACTIONS: Yes - NonUpdate
- ->Install preliminary binary files per HPSBUX01164.
B11.11, B.11.23 running IPSec
set ip_pmtu_strategy = 0 or 3
The binary files and patches cited in the HPSBUX01164 Security
Bulletin will NOT resolve the issue of this Security Bulletin in
the case of the IPSec product.
BULLETIN REVISION HISTORY:
Revision 0: 24 April 2005
Revision 1: 25 May 2005
The binary files of HPSBUX01164 will resolve the issue for
B.11.11 and B.11.23.
Revision 2: 1 June 2005
The binary files of HPSBUX01164 will resolve the issue for the
core TCP/IP in B.11.11, B.11.22, and B.11.23.
The binary files of HPSBUX01164 will resolve NOT resolve the
issue for IPSec.
B.11.00 and B.11.04 are NOT vulnerable.
The recommended workaround is to modify
/etc/rc.config.d/nddconf and reboot.
Revision 3: 27 June 2005
PHNE_33159 is available for B.11.11.
Revision 4: 10 July 2005
PHNE_32606 is available for B.11.23.
Revision 5: 24 July 2005
Corrected description of PMTU to note that the MTU
may as low a 68 bytes.
The action for B.11.11 and B.11.23 core TCP/IP is
to install patches. For B.11.22 the action is to install
preliminary binary files.
Clarified the Resolution and Manual Actions sections.
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HP S/W Security Team
WTEC Cupertino, California