This is a discussion on SSRT5954 rev.2 - HP-UX TCP/IP Remote Denial of Service (DoS) - HP UX ; -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 HP SECURITY BULLETIN HPSBUX01137 REVISION: 2 SSRT5954 rev.2 - HP-UX TCP/IP Remote Denial of Service (DoS) NOTICE: There are no restrictions for distribution of this Security Bulletin provided that it remains complete and intact. ...
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HP SECURITY BULLETIN
HPSBUX01137 REVISION: 2
SSRT5954 rev.2 - 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.
01 June 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.
->action: install preliminary binary files per HPSBUX01164
OR set ip_pmtu_strategy=0 or 3
action: set ip_pmtu_strategy=0 or 3
END AFFECTED VERSIONS
->Note: Setting ip_pmtu_strategy=0 is preferred. Please refer to
HPSBUX01164 for more information.
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
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 requires PHNE_25642 or subsequent in order to set
p_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
Until patches are available the Denial of Service (DoS) can be
avoided by setting the ip_pmtu_strategy parameter to 0 or 3.
->Note: The preliminary binary files cited in HPSBUX01164 for
B.11.11, B.11.22, and B.11.23 will resolve the issue of
this Security Bulletin as well for the core TCP/IP
product. If the IPSec product is installed in B11.11 or
B.11.23 it will still be necessary to work around the
issue of this Security Bulletin by setting
ip_pmtu_strategy=0 or 3.
If the ip_pmtu_strategy value of 3 is desired for B.11.11 apply
the patch 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
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
MANUAL ACTIONS: Yes - NonUpdate
B.11.11, B.11.22, B.11.23
set ip_pmtu_strategy = 0 or 3
->The binary files cited in the HPSBUX01164 Security Bulletin
will resolve the issue of this Security Bulletin as well for the
core TCP/IP product.
->B11.11, B.11.23 running IPSec
->set ip_pmtu_strategy = 0 or 3
->The binary files 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.
HP-UX SPECIFIC SECURITY BULLETINS*: Security Patch Check revision
B.02.00 analyzes all HP-issued Security Bulletins to provide a
subset of recommended actions that potentially affect a specific
For more information:
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* The Software Product Category that this Security Bulletin
relates to is represented by the 5th and 6th characters of the
GN = HP General SW,
MA = HP Management Agents,
MI = Misc. 3rd party SW,
MP = HP MPE/iX,
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System management and security procedures must be reviewed
frequently to maintain system integrity. HP is continually
reviewing and enhancing the security features of software products
to provide customers with current secure solutions.
"HP is broadly distributing this Security Bulletin in order to
bring to the attention of users of the affected HP products the
important security information contained in this Bulletin. HP
recommends that all users determine the applicability of this
information to their individual situations and take appropriate
action. HP does not warrant that this information is necessarily
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(c)Copyright 2005 Hewlett-Packard Development Company, L.P.
Hewlett-Packard Company shall not be liable for technical or
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The information in this document is subject to change without
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HP S/W Security Team
WTEC Cupertino, California