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Recommendations On Filtering IPv4 Packets Containing IPv4 Options

Recommendations On Filtering IPv4 Packets Containing IPv4 Options
Posted Jan 19, 2013
Authored by Fernando Gont

This document document provides advice on the filtering of IPv4 packets based on the IPv4 options they contain. Additionally, it discusses the operational and interoperability implications of dropping packets based on the IP options they contain.

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Recommendations On Filtering IPv4 Packets Containing IPv4 Options

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Operational Security Capabilities for F. Gont
IP Network Infrastructure (opsec) UTN-FRH / SI6 Networks
Internet-Draft R. Atkinson
Intended status: BCP Consultant
Expires: June 17, 2013 C. Pignataro
Cisco
December 14, 2012


Recommendations on filtering of IPv4 packets containing IPv4 options
draft-ietf-opsec-ip-options-filtering-01.txt

Abstract

This document document provides advice on the filtering of IPv4
packets based on the IPv4 options they contain. Additionally, it
discusses the operational and interoperability implications of
dropping packets based on the IP options they contain.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on June 17, 2013.

Copyright Notice

Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of



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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.


Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology and Conventions Used in This Document . . . . 3
2. IP Options . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. General Security Implications of IP options . . . . . . . . . 5
3.1. Processing Requirements . . . . . . . . . . . . . . . . . 5
4. Advice on the Handling of Packets with Specific IP Options . . 5
4.1. End of Option List (Type = 0) . . . . . . . . . . . . . . 5
4.2. No Operation (Type = 1) . . . . . . . . . . . . . . . . . 6
4.3. Loose Source and Record Route (LSRR) (Type = 131) . . . . 7
4.4. Strict Source and Record Route (SSRR) (Type = 137) . . . . 8
4.5. Record Route (Type = 7) . . . . . . . . . . . . . . . . . 9
4.6. Stream Identifier (Type = 136) (obsolete) . . . . . . . . 10
4.7. Internet Timestamp (Type = 68) . . . . . . . . . . . . . . 11
4.8. Router Alert (Type = 148) . . . . . . . . . . . . . . . . 12
4.9. Probe MTU (Type = 11) (obsolete) . . . . . . . . . . . . . 13
4.10. Reply MTU (Type = 12) (obsolete) . . . . . . . . . . . . . 13
4.11. Traceroute (Type = 82) . . . . . . . . . . . . . . . . . . 14
4.12. DoD Basic Security Option (Type = 130) . . . . . . . . . . 14
4.13. DoD Extended Security Option (Type = 133) . . . . . . . . 16
4.14. Commercial IP Security Option (CIPSO) (Type = 134) . . . . 17
4.15. VISA (Type = 142) . . . . . . . . . . . . . . . . . . . . 19
4.16. Extended Internet Protocol (Type = 145) . . . . . . . . . 19
4.17. Address Extension (Type = 147) . . . . . . . . . . . . . . 20
4.18. Sender Directed Multi-Destination Delivery (Type = 149) . 20
4.19. Dynamic Packet State (Type = 151) . . . . . . . . . . . . 21
4.20. Upstream Multicast Pkt. (Type = 152) . . . . . . . . . . . 21
4.21. Quick-Start (Type = 25) . . . . . . . . . . . . . . . . . 22
4.22. RFC3692-style Experiment (Types = 30, 94, 158, and 222) . 23
4.23. Other IP Options . . . . . . . . . . . . . . . . . . . . . 24
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
6. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.1. Normative References . . . . . . . . . . . . . . . . . . . 25
8.2. Informative References . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29









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1. Introduction

This document document discusses the filtering of IPv4 packets based
on the IPv4 options they contain. Since various protocols may use
IPv4 options to some extent, dropping packets based on the options
they contain may have implications on the proper functioning of the
protocol. Therefore, this document attempts to discuss the
operational and interoperability implications of such dropping.
Additionally, it outlines what a network operator might do in a
typical enterprise or Service Provider environments.

We note that data seems to indicate that there is a current
widespread practice of blocking IPv4 optioned packets. There are
various plausible approaches to minimize the potential negative
effects of IPv4 optioned packets while allowing some options
semantics. One approach is to allow for specific options that are
expected or needed, and a default deny. A different approach is to
deny unneeded options and a default allow. Yet a third possible
approach is to allow for end-to-end semantics by ignoring options and
treating packets as un-optioned while in transit. Experiments and
currently-available data tends to support the first or third
approaches as more realistic. Some results of regarding the current
state of affairs with respect to dropping packets containing IP
options can be found in [MEDINA].

We also note that while this document provides advice on dropping
packets on a "per IP option type", not all devices may provide this
capability with such granularity. Additionally, even in cases in
which such functionality is provided, the operator might want to
specify a dropping policy with a coarser granularity (rather than on
a "per IP option type" granularity), as indicated above.

Finally, in scenarios in which processing of IP options by
intermediate systems is not required, a widespread approach is to
simply ignore IP options, and process the corresponding packets as if
they do not contain any IP options.

1.1. Terminology and Conventions Used in This Document

The terms "fast path", "slow path", and associated relative terms
("faster path" and "slower path") are loosely defined as in Section 2
of [RFC6398].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].





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2. IP Options

IP options allow for the extension of the Internet Protocol. As
specified in [RFC0791], there are two cases for the format of an
option:

o Case 1: A single byte of option-type.

o Case 2: An option-type byte, an option-length byte, and the actual
option-data bytes.

IP options of Case 1 have the following syntax:

+-+-+-+-+-+-+-+-+- - - - - - - - -
| option-type | option-data
+-+-+-+-+-+-+-+-+- - - - - - - - -

The length of IP options of Case 1 is implicitly specified by the
option-type byte.

IP options of Case 2 have the following syntax:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| option-type | option-length | option-data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

In this case, the option-length byte counts the option-type byte and
the option-length byte, as well as the actual option-data bytes.

All current and future options except "End of Option List" (Type = 0)
and "No Operation" (Type = 1), are of Class 2.

The option-type has three fields:

o 1 bit: copied flag.

o 2 bits: option class.

o 5 bits: option number.

The copied flag indicates whether this option should be copied to all
fragments in the event the packet carrying it needs to be fragmented:

o 0 = not copied.

o 1 = copied.

The values for the option class are:



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o 0 = control.

o 1 = reserved for future use.

o 2 = debugging and measurement.

o 3 = reserved for future use.

This format allows for the creation of new options for the extension
of the Internet Protocol (IP).

Finally, the option number identifies the syntax of the rest of the
option.

The "IP OPTION NUMBERS" registry [IANA-IP] contains the list of the
currently assigned IP option numbers.


3. General Security Implications of IP options

3.1. Processing Requirements

Router architectures can perform IP option processing in a slower
path. Unless protective measures are taken, this represents a
potential Denial of Service (DoS) risk, as there is possibility for
the option processing to overwhelm the router's CPU or the protocols
processed in the router's slow path. Additional considerations for
protecting the router control plane from IP optioned packets can be
found in [RFC6192].


4. Advice on the Handling of Packets with Specific IP Options

The following subsections contain a description of each of the IP
options that have so far been specified, a discussion of possible
interoperability implications if packets containing such options are
dropped, and specific advice on whether to drop packets containing
these options in a typical enterprise or Service Provider
environment.

4.1. End of Option List (Type = 0)

4.1.1. Uses

This option is used to indicate the "end of options" in those cases
in which the end of options would not coincide with the end of the
Internet Protocol Header.




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4.1.2. Option Specification

Specified in RFC 791 [RFC0791].

4.1.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.1.4. Operational and Interoperability Impact if Blocked

Packets containing any IP options are likely to include an End of
Option List. Therefore, if packets containing this option are
dropped, it is very likely that legitimate traffic is blocked.

4.1.5. Advice

Routers, security gateways, and firewalls SHOULD NOT drop packets
containing this option.

4.2. No Operation (Type = 1)

4.2.1. Uses

The no-operation option is basically meant to allow the sending
system to align subsequent options in, for example, 32-bit
boundaries.

4.2.2. Option Specification

Specified in RFC 791 [RFC0791].

4.2.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.2.4. Operational and Interoperability Impact if Blocked

Packets containing any IP options are likely to include a No
Operation option. Therefore, if packets containing this option are
dropped, it is very likely that legitimate traffic is blocked.

4.2.5. Advice

Routers, security gateways, and firewalls SHOULD NOT drop packets
containing this option.




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4.3. Loose Source and Record Route (LSRR) (Type = 131)

RFC 791 states that this option should appear, at most, once in a
given packet. Thus, if a packet contains more than one LSRR option,
it should be dropped, and this event should be logged (e.g., a
counter could be incremented to reflect the packet drop).
Additionally, packets containing a combination of LSRR and SSRR
options should be dropped, and this event should be logged (e.g., a
counter could be incremented to reflect the packet drop).

4.3.1. Uses

This option lets the originating system specify a number of
intermediate systems a packet must pass through to get to the
destination host. Additionally, the route followed by the packet is
recorded in the option. The receiving host (end-system) must use the
reverse of the path contained in the received LSRR option.

The LSSR option can be of help in debugging some network problems.
Some ISP (Internet Service Provider) peering agreements require
support for this option in the routers within the peer of the ISP.

4.3.2. Option Specification

Specified in RFC 791 [RFC0791].

4.3.3. Threats

The LSRR option has well-known security implications. Among other
things, the option can be used to:

o Bypass firewall rules

o Reach otherwise unreachable internet systems

o Establish TCP connections in a stealthy way

o Learn about the topology of a network

o Perform bandwidth-exhaustion attacks

Of these attack vectors, the one that has probably received least
attention is the use of the LSRR option to perform bandwidth
exhaustion attacks. The LSRR option can be used as an amplification
method for performing bandwidth-exhaustion attacks, as an attacker
could make a packet bounce multiple times between a number of systems
by carefully crafting an LSRR option.




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This is the IPv4-version of the IPv6 amplification attack that was
widely publicized in 2007 [Biondi2007]. The only difference is
that the maximum length of the IPv4 header (and hence the LSRR
option) limits the amplification factor when compared to the IPv6
counter-part.

Additionally, some implementations have been found to fail to include
proper sanity checks on the LSRR option, thus leading to security
issues.

[Microsoft1999] is a security advisory about a vulnerability
arising from improper validation of the Pointer field of the LSRR
option.

Finally, we note that some systems were known for providing a system-
wide toggle to enable support for this option for those scenarios in
which this option is required. However, improper implementation of
such system-wide toggle caused those systems to support the LSRR
option even when explicitly configured not to do so.

[OpenBSD1998] is a security advisory about an improper
implementation of such a system-wide toggle in 4.4BSD kernels.

4.3.4. Operational and Interoperability Impact if Blocked

Network troubleshooting techniques that may employ the LSRR option
(such as ping or traceroute) would break. Nevertheless, it should be
noted that it is virtually impossible to use the LSRR option for
troubleshooting, due to widespread dropping of packets that contain
such option.

4.3.5. Advice

Routers, security gateways, and firewalls SHOULD, by default, drop IP
packets that contain an LSRR option.

4.4. Strict Source and Record Route (SSRR) (Type = 137)

4.4.1. Uses

This option allows the originating system to specify a number of
intermediate systems a packet must pass through to get to the
destination host. Additionally, the route followed by the packet is
recorded in the option, and the destination host (end-system) must
use the reverse of the path contained in the received SSRR option.

This option is similar to the Loose Source and Record Route (LSRR)
option, with the only difference that in the case of SSRR, the route



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specified in the option is the exact route the packet must take
(i.e., no other intervening routers are allowed to be in the route).

The SSSR option can be of help in debugging some network problems.
Some ISP (Internet Service Provider) peering agreements require
support for this option in the routers within the peer of the ISP.

4.4.2. Option Specification

Specified in RFC 791 [RFC0791].

4.4.3. Threats

The SSRR option has the same security implications as the LSRR
option. Please refer to Section 4.3 for a discussion of such
security implications.

4.4.4. Operational and Interoperability Impact if Blocked

Network troubleshooting techniques that may employ the SSRR option
(such as ping or traceroute) would break. Nevertheless, it should be
noted that it is virtually impossible to use the SSR option for
trouble-shooting, due to widespread dropping of packets that contain
such option.

4.4.5. Advice

Routers, security gateways, and firewalls SHOULD, by default, drop IP
packets that contain an SSRR option.

4.5. Record Route (Type = 7)

4.5.1. Uses

This option provides a means to record the route that a given packet
follows.

4.5.2. Option Specification

Specified in RFC 791 [RFC0791].

4.5.3. Threats

This option can be exploited to map the topology of a network.
However, the limited space in the IP header limits the usefulness of
this option for that purpose.





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4.5.4. Operational and Interoperability Impact if Blocked

Network troubleshooting techniques that may employ the RR option
(such as ping with the RR option) would break. Nevertheless, it
should be noted that it is virtually impossible to use such
techniques due to widespread dropping of packets that contain RR
options.

4.5.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets
containing a Record Route option.

4.6. Stream Identifier (Type = 136) (obsolete)

The Stream Identifier option originally provided a means for the 16-
bit SATNET stream Identifier to be carried through networks that did
not support the stream concept.

However, as stated by Section 3.2.1.8 of RFC 1122 [RFC1122] and
Section 4.2.2.1 of RFC 1812 [RFC1812], this option is obsolete.
Therefore, it must be ignored by the processing systems. See also
Section 5.

RFC 791 states that this option appears at most once in a given
datagram. Therefore, if a packet contains more than one instance of
this option, it should be dropped, and this event should be logged
(e.g., a counter could be incremented to reflect the packet drop).

4.6.1. Uses

This option is obsolete. There is no current use for this option.

4.6.2. Option Specification

Specified in RFC 791 [RFC0791], and obsoleted in RFC 1122 [RFC1122]
and RFC 1812 [RFC1812].

4.6.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.6.4. Operational and Interoperability Impact if Blocked

None.





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4.6.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets
containing a Stream Identifier option.

4.7. Internet Timestamp (Type = 68)

4.7.1. Uses

This option provides a means for recording the time at which each
system processed this datagram.

4.7.2. Option Specification

Specified by RFC 791 [RFC0791].

4.7.3. Threats

The timestamp option has a number of security implications. Among
them are:

o It allows an attacker to obtain the current time of the systems
that process the packet, which the attacker may find useful in a
number of scenarios.

o It may be used to map the network topology, in a similar way to
the IP Record Route option.

o It may be used to fingerprint the operating system in use by a
system processing the datagram.

o It may be used to fingerprint physical devices, by analyzing the
clock skew.

[Kohno2005] describes a technique for fingerprinting devices by
measuring the clock skew. It exploits, among other things, the
timestamps that can be obtained by means of the ICMP timestamp
request messages [RFC0791]. However, the same fingerprinting method
could be implemented with the aid of the Internet Timestamp option.

4.7.4. Operational and Interoperability Impact if Blocked

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.







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4.7.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets
containing an Internet Timestamp option.

4.8. Router Alert (Type = 148)

4.8.1. Uses

The Router Alert option has the semantic "routers should examine this
packet more closely, if they participate in the functionality denoted
by the Value of the option".

4.8.2. Option Specification

The Router Alert option is defined in RFC 2113 [RFC2113] and later
updates to it have been clarified by RFC 5350 [RFC5350]. It contains
a 16-bit Value governed by an IANA registry (see [RFC5350]).

4.8.3. Threats

The security implications of the Router Alert option have been
discussed in detail in [RFC6398]. Basically, the Router Alert option
might be exploited to perform a Denial of Service (DoS) attack by
exhausting CPU resources at the processing routers.

4.8.4. Operational and Interoperability Impact if Blocked

Applications that employ the Router Alert option (such as RSVP
[RFC2205]) would break.

4.8.5. Advice

This option SHOULD be allowed only in controlled environments, where
the option can be used safely. [RFC6398] identifies some such
environments. In unsafe environments, packets containing this option
SHOULD be dropped.

A given router, security gateway, or firewall system has no way of
knowing a priori whether this option is valid in its operational
environment. Therefore, routers, security gateways, and firewalls
SHOULD, by default, ignore the Router Alert option. Additionally,
Routers, security gateways, and firewalls SHOULD have a configuration
setting that indicates whether they should react act on the Router
Alert option as indicated in the corresponding specification or
ignore the option, or whether packets containing this option should
be dropped (with the default configuration being to ignore the Router
Alert option).



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4.9. Probe MTU (Type = 11) (obsolete)

4.9.1. Uses

This option originally provided a mechanism to discover the Path-MTU.
It has been declared obsolete.

4.9.2. Option Specification

This option was originally defined in RFC 1063 [RFC1063], and was
obsoleted with RFC 1191 [RFC1191]. This option is now obsolete, as
RFC 1191 obsoletes RFC 1063 without using IP options.

4.9.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.9.4. Operational and Interoperability Impact if Blocked

None

4.9.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain a Probe MTU option.

4.10. Reply MTU (Type = 12) (obsolete)

4.10.1. Uses

This option and originally provided a mechanism to discover the Path-
MTU. It is now obsolete.

4.10.2. Option Specification

This option was originally defined in RFC 1063 [RFC1063], and was
obsoleted with RFC 1191 [RFC1191]. This option is now obsolete, as
RFC 1191 obsoletes RFC 1063 without using IP options.

4.10.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.







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4.10.4. Operational and Interoperability Impact if Blocked

None

4.10.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain a Reply MTU option.

4.11. Traceroute (Type = 82)

4.11.1. Uses

This option originally provided a mechanism to trace the path to a
host.

4.11.2. Option Specification

This option was originally specified by RFC 1393 [RFC1393]. The
Traceroute option is defined as "experimental" and it was never
widely deployed on the public Internet.

4.11.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.11.4. Operational and Interoperability Impact if Blocked

None

4.11.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain a Traceroute option.

4.12. DoD Basic Security Option (Type = 130)

4.12.1. Uses

This option is used by Multi-Level-Secure (MLS) end-systems and
intermediate systems in specific environments to [RFC1108]:

o Transmit from source to destination in a network standard
representation the common security labels required by computer
security models [Landwehr81],





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o Validate the datagram as appropriate for transmission from the
source and delivery to the destination, and,

o Ensure that the route taken by the datagram is protected to the
level required by all protection authorities indicated on the
datagram.

The DoD Basic Security Option (BSO) is currently implemented in a
number of operating systems (e.g., [IRIX2008], [SELinux2008],
[Solaris2008], and [Cisco-IPSO]), and deployed in a number of high-
security networks. These networks are typically either in physically
secure locations, protected by military/governmental communications
security equipment, or both. Such networks are typically built using
commercial off-the-shelf (COTS) IP routers and Ethernet switches, but
are not normally interconnected with the global public Internet.
This option probably has more deployment now than when the IESG
removed this option from the IETF standards-track. [RFC5570]
describes a similar option recently defined for IPv6 and has much
more detailed explanations of how sensitivity label options are used
in real-world deployments.

4.12.2. Option Specification

It is specified by RFC 1108 [RFC1108]], which obsoleted RFC 1038
[RFC1038] (which in turn obsoleted the Security Option defined in RFC
791 [RFC0791]).

RFC 791 [RFC0791] defined the "Security Option" (Type = 130),
which used the same option type as the DoD Basic Security option
discussed in this section. Later, RFC 1038 [RFC1038] revised the
IP security options, and in turn was obsoleted by RFC 1108
[RFC1108]. The "Security Option" specified in RFC 791 is
considered obsolete by Section 3.2.1.8 of RFC 1122 [RFC1122] and
Section 4.2.2.1 of RFC 1812 [RFC1812], and therefore the
discussion in this section is focused on the DoD Basic Security
option specified by RFC 1108 [RFC1108].

Section 4.2.2.1 of RFC 1812 states that routers "SHOULD implement
this option".

Many Cisco routers that run Cisco IOS include support dropping
packets that contain this option with per-interface granularity.
This capability has been present in many Cisco routers since the
early 1990s [Cisco-IPSO-Cmds]. Some governmental products
reportedly support BSO, notably CANEWARE [RFC4949]. Support for
BSO is included in the "IPsec Configuration Policy Information
Model" [RFC3585] and in the "IPsec Security Policy Database
Configuration MIB" [RFC4807].



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4.12.3. Threats

Presence of this option in a packet does not by itself create any
specific new threat (other than the usual generic issues that might
be created if packets with options are forwarded via the "slow
path"). Packets with this option ought not normally be seen on the
global public Internet.

4.12.4. Operational and Interoperability Impact if Blocked

If packets with this option are blocked or if the option is stripped
from the packet during transmission from source to destination, then
the packet itself is likely to be dropped by the receiver because it
isn't properly labelled. In some cases, the receiver might receive
the packet but associate an incorrect sensitivity label with the
received data from the packet whose BSO was stripped by an
intermediate router or firewall. Associating an incorrect
sensitivity label can cause the received information either to be
handled as more sensitive than it really is ("upgrading") or as less
sensitive than it really is ("downgrading"), either of which is
problematic.

4.12.5. Advice

Routers, security gateways, and firewalls SHOULD NOT by default
modify or remove this option from IP packets and SHOULD NOT by
default drop packets containing this option. For auditing reasons,
Routers, security gateways, and firewalls SHOULD be capable of
logging the numbers of packets containing the BSO on a per-interface
basis. Also, Routers, security gateways, and firewalls SHOULD be
capable of dropping packets based on the BSO presence as well as the
BSO values.

4.13. DoD Extended Security Option (Type = 133)

4.13.1. Uses

This option permits additional security labeling information, beyond
that present in the Basic Security Option (Section 4.12), to be
supplied in an IP datagram to meet the needs of registered
authorities.

4.13.2. Option Specification

The DoD Extended Security Option (ESO) is specified by RFC 1108
[RFC1108].





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Many Cisco routers that run Cisco IOS include support for dropping
packets that contain this option with a per-interface granularity.
This capability has been present in many Cisco routers since the
early 1990s [Cisco-IPSO-Cmds]. Some governmental products
reportedly support ESO, notably CANEWARE [RFC4949]. Support for
ESO is included in the "IPsec Configuration Policy Information
Model" [RFC3585] and in the "IPsec Security Policy Database
Configuration MIB" [RFC4807].

4.13.3. Threats

Presence of this option in a packet does not by itself create any
specific new threat (other than the usual generic issues that might
be created if packets with options are forwarded via the "slow
path"). Packets with this option ought not normally be seen on the
global public Internet

4.13.4. Operational and Interoperability Impact if Blocked

If packets with this option are blocked or if the option is stripped
from the packet during transmission from source to destination, then
the packet itself is likely to be dropped by the receiver because it
isn't properly labelled. In some cases, the receiver might receive
the packet but associate an incorrect sensitivity label with the
received data from the packet whose ESO was stripped by an
intermediate router or firewall. Associating an incorrect
sensitivity label can cause the received information either to be
handled as more sensitive than it really is ("upgrading") or as less
sensitive than it really is ("downgrading"), either of which is
problematic.

4.13.5. Advice

Routers, security gateways, and firewalls SHOULD NOT by default
modify or remove this option from IP packets and SHOULD NOT by
default drop packets containing this option. For auditing reasons,
Routers, security gateways, and firewalls SHOULD be capable of
logging the numbers of packets containing the ESO on a per-interface
basis. Also, Routers, security gateways, and firewalls SHOULD be
capable of dropping packets based on the ESO presence as well as the
ESO values.

4.14. Commercial IP Security Option (CIPSO) (Type = 134)

4.14.1. Uses

This option was proposed by the Trusted Systems Interoperability
Group (TSIG), with the intent of meeting trusted networking



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requirements for the commercial trusted systems market place.

It is currently implemented in a number of operating systems (e.g.,
IRIX [IRIX2008], Security-Enhanced Linux [SELinux2008], and Solaris
[Solaris2008]), and deployed in a number of high-security networks.

4.14.2. Option Specification

This option is specified in [CIPSO1992] and [FIPS1994]. There are
zero known IP router implementations of CIPSO. Several MLS operating
systems support CIPSO, generally the same MLS operating systems that
support IPSO.

The TSIG proposal was taken to the Commercial Internet Security
Option (CIPSO) Working Group of the IETF [CIPSOWG1994], and an
Internet-Draft was produced [CIPSO1992]. The Internet-Draft was
never published as an RFC, but the proposal was later standardized
by the U.S. National Institute of Standards and Technology (NIST)
as "Federal Information Processing Standard Publication 188"
[FIPS1994].

4.14.3. Threats

Presence of this option in a packet does not by itself create any
specific new threat (other than the usual generic issues that might
be created if packets with options are forwarded via the "slow
path"). Packets with this option ought not normally be seen on the
global public Internet.

4.14.4. Operational and Interoperability Impact if Blocked

If packets with this option are blocked or if the option is stripped
from the packet during transmission from source to destination, then
the packet itself is likely to be dropped by the receiver because it
isn't properly labelled. In some cases, the receiver might receive
the packet but associate an incorrect sensitivity label with the
received data from the packet whose CIPSO was stripped by an
intermediate router or firewall. Associating an incorrect
sensitivity label can cause the received information either to be
handled as more sensitive than it really is ("upgrading") or as less
sensitive than it really is ("downgrading"), either of which is
problematic.

4.14.5. Advice

Because of the design of this option, with variable syntax and
variable length, it is not practical to support specialized filtering
using the CIPSO information. No routers or firewalls are known to



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support this option. However, Routers, security gateways, and
firewalls SHOULD NOT by default modify or remove this option from IP
packets and SHOULD NOT by default drop packets containing this
option.

4.15. VISA (Type = 142)

4.15.1. Uses

This options was part of an experiment at USC and was never widely
deployed.

4.15.2. Option Specification

Not publicly available.

4.15.3. Threats

Not possible to determine (other the general security implications of
IP options discussed in Section 3), since the corresponding
specification is not publicly available.

4.15.4. Operational and Interoperability Impact if Blocked

None.

4.15.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain this option.

4.16. Extended Internet Protocol (Type = 145)

4.16.1. Uses

The EIP option was introduced by one of the proposals submitted
during the IPng efforts to address the problem of IPv4 address
exhaustion.

4.16.2. Option Specification

Specified in [RFC1385]. This option has been formally obsoleted by
[RFC6814].

4.16.3. Threats

There are no know threats arising from this option, other than the
general security implications of IP options discussed in Section 3.



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4.16.4. Operational and Interoperability Impact if Blocked

None.

4.16.5. Advice

Routers, security gateways, and firewalls SHOULD drop packets that
contain this option.

4.17. Address Extension (Type = 147)

4.17.1. Uses

The Address Extension option was introduced by one of the proposals
submitted during the IPng efforts to address the problem of IPv4
address exhaustion.

4.17.2. Option Specification

Specified in [RFC1475]. This option has been formally obsoleted by
[RFC6814].

4.17.3. Threats

There are no know threats arising from this option, other than the
general security implications of IP options discussed in Section 3.

4.17.4. Operational and Interoperability Impact if Blocked

None.

4.17.5. Advice

Routers, security gateways, and firewalls SHOULD drop packets that
contain this option.

4.18. Sender Directed Multi-Destination Delivery (Type = 149)

4.18.1. Uses

This option originally provided unreliable UDP delivery to a set of
addresses included in the option.

4.18.2. Option Specification

This option is defined in RFC 1770 [RFC1770].





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4.18.3. Threats

This option could have been exploited for bandwidth-amplification in
Denial of Service (DoS) attacks.

4.18.4. Operational and Interoperability Impact if Blocked

None.

4.18.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain a Sender Directed Multi-Destination Delivery option.

4.19. Dynamic Packet State (Type = 151)

4.19.1. Uses

The Dynamic Packet State option was used to specify specified Dynamic
Packet State (DPS) in the context of the differentiated service
architecture.

4.19.2. Option Specification

The Dynamic Packet State option was specified in
[I-D.stoica-diffserv-dps]. The aforementioned document was meant to
be published as "Experimental", but never made it into an RFC. This
option has been formally obsoleted by [RFC6814].

4.19.3. Threats

Possible threats include theft of service and Denial of Service.
However, we note that is option has never been widely implemented or
deployed.

4.19.4. Operational and Interoperability Impact if Blocked

None.

4.19.5. Advice

Routers, security gateways, and firewalls SHOULD drop packets that
contain this option.

4.20. Upstream Multicast Pkt. (Type = 152)






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4.20.1. Uses

This option was meant to solve the problem of doing upstream
forwarding of multicast packets on a multi-access LAN.

4.20.2. Option Specification

This option was originally specified in [draft-farinacci-bidir-pim].
Its use was obsoleted by [RFC5015], which employs a control plane
mechanism to solve the problem of doing upstream forwarding of
multicast packets on a multi-access LAN. This option has been
formally obsoleted by [RFC6814].

4.20.3. Threats

TBD.

4.20.4. Operational and Interoperability Impact if Blocked

None.

4.20.5. Advice

Routers, security gateways, and firewalls SHOULD drop packets that
contain this option.

4.21. Quick-Start (Type = 25)

4.21.1. Uses

This IP Option is used in the specification of Quick-Start for TCP
and IP, which is an experimental mechanism that allows transport
protocols, in cooperation with routers, to determine an allowed
sending rate at the start and, at times, in the middle of a data
transfer (e.g., after an idle period) [RFC4782].

4.21.2. Option Specification

Specified in RFC 4782 [RFC4782], on the "Experimental" track.

4.21.3. Threats

Section 9.6 of [RFC4782] notes that Quick-Start is vulnerable to two
kinds of attacks:

o attacks to increase the routers' processing and state load, and,





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o attacks with bogus Quick-Start Requests to temporarily tie up
available Quick-Start bandwidth, preventing routers from approving
Quick-Start Requests from other connections

4.21.4. Operational and Interoperability Impact if Blocked

The Quick-Start functionality would be disabled, and additional
delays in e.g. TCP's connection establishment could be introduced
(please see Section 4.7.2 of [RFC4782]. We note, however, that
Quick-Start has been proposed as mechanism that could be of use in
controlled environments, and not as a mechanism that would be
intended or appropriate for ubiquitous deployment in the global
Internet [RFC4782].

4.21.5. Advice

A given router, security gateway, or firewall system has no way of
knowing a priori whether this option is valid in its operational
environment. Therefore, routers, security gateways, and firewalls
SHOULD, by default, ignore the Quick Start option. Additionally,
routers, security gateways, and firewalls SHOULD have a configuration
setting that indicates whether they should react act on the Quick
Start option as indicated in the corresponding specification or
ignore the option, or whether packets containing this option should
be dropped (with the default configuration being to ignore the Quick
Start option).

We note that if routers in a given environment do not implement
and enable the Quick-Start mechanism, only the general security
implications of IP options (discussed in Section 3) would apply.

4.22. RFC3692-style Experiment (Types = 30, 94, 158, and 222)

Section 2.5 of RFC 4727 [RFC4727] allocates an option number with all
defined values of the "copy" and "class" fields for RFC3692-style
experiments. This results in four distinct option type codes: 30,
94, 158, and 222.

4.22.1. Uses

It is only appropriate to use these values in explicitly-configured
experiments; they MUST NOT be shipped as defaults in implementations.

4.22.2. Option Specification

Specified in RFC 4727 [RFC4727] in the context of RFC3692-style
experiments.




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4.22.3. Threats

No security issues are known for this option, other than the general
security implications of IP options discussed in Section 3.

4.22.4. Operational and Interoperability Impact if Blocked

None.

4.22.5. Advice

Routers, security gateways, and firewalls SHOULD drop IP packets that
contain RFC3692-style Experiment options.

4.23. Other IP Options

Unrecognized IP Options are to be ignored. Section 3.2.1.8 of RFC
1122 [RFC1122] and Section 4.2.2.6 of RFC 1812 [RFC1812] specify this
behavior as follows:

RFC 1122: "The IP and transport layer MUST each interpret those IP
options that they understand and silently ignore the
others."

RFC 1812: "A router MUST ignore IP options which it does not
recognize."

This document adds that unrecognized IP Options MAY also be logged.

A number of additional options are specified in the "IP OPTIONS
NUMBERS" IANA registry [IANA-IP]. Specifically:

Copy Class Number Value Name Reference
---- ----- ------ ----- ------------------------------- ------------
0 0 10 10 ZSU - Experimental Measurement [ZSu]
1 2 13 205 FINN - Experimental Flow Control [Finn]
0 0 15 15 ENCODE - ??? [VerSteeg]
1 0 16 144 IMITD - IMI Traffic Descriptor [Lee]
1 0 22 150 - Unassigned (Released 18 Oct. 2005)


5. IANA Considerations

This document has no actions for IANA.







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6. Security Considerations

This document provides advice on the filtering of IP packets that
contain IP options. Dropping such packets can help to mitigate the
security issues that arise from use of different IP options.


7. Acknowledgements

The authors would like to thank Panos Kampanakis and Donald Smith for
providing valuable comments on earlier versions of this document.

Part of this document is based on the document "Security Assessment
of the Internet Protocol" [CPNI2008] that is the result of a project
carried out by Fernando Gont on behalf of UK CPNI (formerly NISCC).

Fernando Gont would like to thank UK CPNI (formerly NISCC) for their
continued support.


8. References

8.1. Normative References

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.

[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.

[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.

[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.

[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006.

[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.



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8.2. Informative References

[Biondi2007]
Biondi, P. and A. Ebalard, "IPv6 Routing Header Security",
CanSecWest 2007 Security Conference <http://
www.secdev.org/conf/IPv6_RH_security-csw07.pdf>, 2007.

[CIPSO1992]
CIPSO, "COMMERCIAL IP SECURITY OPTION (CIPSO 2.2)",
draft-ietf-cipso-ipsecurity-01 (work in progress), 1992.

[CIPSOWG1994]
CIPSOWG, "Commercial Internet Protocol Security Option
(CIPSO) Working Group", 1994, <http://www.ietf.org/
proceedings/94jul/charters/cipso-charter.html>.

[CPNI2008]
Gont, F., "Security Assessment of the Internet Protocol",
<http://www.cpni.gov.uk/Docs/InternetProtocol.pdf>, 2008.

[Cisco-IPSO]
Cisco Systems, Inc., "Cisco IOS Security Configuration
Guide, Release 12.2 - Configuring IP Security Options", <
http://www.cisco.com/en/US/docs/ios/12_2/security/
configuration/guide/scfipso.html>, 2006.

[Cisco-IPSO-Cmds]
Cisco Systems, Inc., "Cisco IOS Security Command
Reference, Release 12.2 - IP Security Options Commands",
<http://www.cisco.com/en/US/docs/ios/12_2/security/
command/reference/srfipso.html>.

[FIPS1994]
FIPS, "Standard Security Label for Information Transfer",
Federal Information Processing Standards Publication. FIP
PUBS 188, <http://csrc.nist.gov/publications/fips/
fips188/fips188.pdf>, 1994.

[I-D.stoica-diffserv-dps]
Stoica, I., Zhang, H., Baker, F., and Y. Bernet, "Per Hop
Behaviors Based on Dynamic Packet State",
draft-stoica-diffserv-dps-02 (work in progress),
October 2002.

[IANA-IP] Internet Assigned Numbers Authority, "IP OPTION NUMBERS",
April 2011,
<http://www.iana.org/assignments/ip-parameters>.




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[IRIX2008]
IRIX, "IRIX 6.5 trusted_networking(7) manual page", <http
://techpubs.sgi.com/library/tpl/cgi-bin/
getdoc.cgi?coll=0650&db=man&fname=/usr/share/catman/a_man/
cat7/trusted_networking.z>, 2008.

[Kohno2005]
Kohno, T., Broido, A., and kc. Claffy, "Remote Physical
Device Fingerprinting", IEEE Transactions on Dependable
and Secure Computing Vol. 2, No. 2, 2005.

[Landwehr81]
Landwehr, C., "Formal Models for Computer Security", ACM
Computing Surveys Vol 13, No 3, September 1981, Assoc for
Computing Machinery, New York, NY, USA, 1981.

[MEDINA] Medina, A., Allman, M., and S. Floyd, "Measuring
Interactions Between Transport Protocols and Middleboxes",
Proc. 4th ACM SIGCOMM/USENIX Conference on
Internet Measurement, October 2004.

[Microsoft1999]
Microsoft, "Microsoft Security Program: Microsoft Security
Bulletin (MS99-038). Patch Available for "Spoofed Route
Pointer" Vulnerability", 1999, <http://www.microsoft.com/
technet/security/bulletin/ms99-038.mspx>.

[OpenBSD1998]
OpenBSD, "OpenBSD Security Advisory: IP Source Routing
Problem", 1998,
<http://www.openbsd.org/advisories/sourceroute.txt>.

[RFC1038] St. Johns, M., "Draft revised IP security option",
RFC 1038, January 1988.

[RFC1063] Mogul, J., Kent, C., Partridge, C., and K. McCloghrie, "IP
MTU discovery options", RFC 1063, July 1988.

[RFC1108] Kent, S., "U.S", RFC 1108, November 1991.

[RFC1385] Wang, Z., "EIP: The Extended Internet Protocol", RFC 1385,
November 1992.

[RFC1393] Malkin, G., "Traceroute Using an IP Option", RFC 1393,
January 1993.

[RFC1475] Ullmann, R., "TP/IX: The Next Internet", RFC 1475,
June 1993.



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[RFC1770] Graff, C., "IPv4 Option for Sender Directed Multi-
Destination Delivery", RFC 1770, March 1995.

[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.

[RFC3585] Jason, J., Rafalow, L., and E. Vyncke, "IPsec
Configuration Policy Information Model", RFC 3585,
August 2003.

[RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, January 2007.

[RFC4807] Baer, M., Charlet, R., Hardaker, W., Story, R., and C.
Wang, "IPsec Security Policy Database Configuration MIB",
RFC 4807, March 2007.

[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.

[RFC5350] Manner, J. and A. McDonald, "IANA Considerations for the
IPv4 and IPv6 Router Alert Options", RFC 5350,
September 2008.

[RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)",
RFC 5570, July 2009.

[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, March 2011.

[RFC6398] Le Faucheur, F., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, October 2011.

[RFC6814] Pignataro, C. and F. Gont, "Formally Deprecating Some IPv4
Options", RFC 6814, November 2012.

[SELinux2008]
Security Enhanced Linux, "http://www.nsa.gov/selinux/".

[Solaris2008]
Solaris Trusted Extensions - Labeled Security for Absolute
Protection, "http://www.sun.com/software/solaris/ds/
trusted_extensions.jsp#3", 2008.

[draft-farinacci-bidir-pim]
Estrin, D. and D. Farinacci, "Bi-Directional Shared Trees



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in PIM-SM", IETF Internet Draft,
draft-farinacci-bidir-pim, work in progress, May 1999.


Authors' Addresses

Fernando Gont
UTN-FRH / SI6 Networks
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina

Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com


RJ Atkinson
Consultant
McLean, VA 22103
USA

Email: rja.lists@gmail.com


Carlos Pignataro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US

Email: cpignata@cisco.com



















Gont, et al. Expires June 17, 2013 [Page 29]

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