HP SECURITY BULLETIN
 
HPSBUX01137     REVISION: 0
 
SSRT5954 rev.0 - 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.
	
 
The information in this Security Bulletin should be acted upon as soon as possible.
INITIAL RELEASE:   	
 
24 April 2005 
 
POTENTIAL SECURITY IMPACT:   	
 
Remote Denial of Service (DoS)
SOURCE:   	
 
Hewlett-Packard Company
HP Software Security Response Team
VULNERABILITY SUMMARY:
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 (DoS).
REFERENCES:   	
 
CAN-2005-1192
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).
BACKGROUND:
For a PGP signed version of this Security Bulletin please write to
security-alert@hp.com.
 
     AFFECTED VERSIONS
 
     HP-UX B.11.23
     HP-UX B.11.22
     HP-UX B.11.11
     HP-UX B.11.04
     HP-UX B.11.00
     =============
     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 takes effect.
 
Note:
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.
 
Note:
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
RESOLUTION:
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:
 
TRANSPORT_NAME[n]=ip
NDD_NAME[n]=ip_pmtu_strategy
NDD_VALUE[n]=0
 
or
 
TRANSPORT_NAME[n]=ip
NDD_NAME[n]=ip_pmtu_strategy
NDD_VALUE[n]=3
 
where 'n' is the next available index value as described in the nddconf comments.
 
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
 
or
 
  /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
  Initial release
 
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