draft-ietf-6man-stable-privacy-addresses-10.txt   draft-ietf-6man-stable-privacy-addresses-11.txt 
IPv6 maintenance Working Group (6man) F. Gont IPv6 maintenance Working Group (6man) F. Gont
Internet-Draft SI6 Networks / UTN-FRH Internet-Draft SI6 Networks / UTN-FRH
Intended status: Standards Track June 12, 2013 Intended status: Standards Track August 8, 2013
Expires: December 14, 2013 Expires: February 9, 2014
A method for Generating Stable Privacy-Enhanced Addresses with IPv6 A method for Generating Stable Privacy-Enhanced Addresses with IPv6
Stateless Address Autoconfiguration (SLAAC) Stateless Address Autoconfiguration (SLAAC)
draft-ietf-6man-stable-privacy-addresses-10 draft-ietf-6man-stable-privacy-addresses-11
Abstract Abstract
This document specifies a method for generating IPv6 Interface This document specifies a method for generating IPv6 Interface
Identifiers to be used with IPv6 Stateless Address Autoconfiguration Identifiers to be used with IPv6 Stateless Address Autoconfiguration
(SLAAC), such that addresses configured using this method are stable (SLAAC), such that addresses configured using this method are stable
within each subnet, but the Interface Identifier changes when hosts within each subnet, but the Interface Identifier changes when hosts
move from one network to another. This method is meant to be an move from one network to another. This method is meant to be an
alternative to generating Interface Identifiers based on hardware alternative to generating Interface Identifiers based on hardware
address (e.g., using IEEE identifiers), such that the benefits of address (e.g., using IEEE identifiers), such that the benefits of
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This Internet-Draft will expire on December 14, 2013. This Internet-Draft will expire on February 9, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Design goals . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Design goals . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Algorithm specification . . . . . . . . . . . . . . . . . . . 8 3. Algorithm specification . . . . . . . . . . . . . . . . . . . 9
4. Resolving Duplicate Address Detection (DAD) conflicts . . . . 13 4. Resolving Duplicate Address Detection (DAD) conflicts . . . . 14
5. Specified Constants . . . . . . . . . . . . . . . . . . . . . 14 5. Specified Constants . . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . . 19 9.1. Normative References . . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . . 21
Appendix A. Possible sources for the Net_Iface parameter . . . . 22 Appendix A. Possible sources for the Net_Iface parameter . . . . 23
A.1. Interface Index . . . . . . . . . . . . . . . . . . . . . 22 A.1. Interface Index . . . . . . . . . . . . . . . . . . . . . 23
A.2. Interface Name . . . . . . . . . . . . . . . . . . . . . . 22 A.2. Interface Name . . . . . . . . . . . . . . . . . . . . . . 23
A.3. Link-layer Addresses . . . . . . . . . . . . . . . . . . . 22 A.3. Link-layer Addresses . . . . . . . . . . . . . . . . . . . 23
A.4. Logical Network Service Identity . . . . . . . . . . . . . 23 A.4. Logical Network Service Identity . . . . . . . . . . . . . 24
Appendix B. Security/privacy issues with traditional SLAAC Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25
addresses . . . . . . . . . . . . . . . . . . . . . . 24
B.1. Correlation of node activities within the same network . . 24
B.2. Correlation of node activities across networks (host
tracking) . . . . . . . . . . . . . . . . . . . . . . . . 24
B.3. Address-scanning attacks . . . . . . . . . . . . . . . . . 25
B.4. Exploitation of device-specific information . . . . . . . 25
Appendix C. Privacy issues still present when temporary
addresses are employed . . . . . . . . . . . . . . . 26
C.1. Host tracking . . . . . . . . . . . . . . . . . . . . . . 26
C.1.1. Tracking hosts across networks #1 . . . . . . . . . . 26
C.1.2. Tracking hosts across networks #2 . . . . . . . . . . 27
C.1.3. Revealing the identity of devices performing
server-like functions . . . . . . . . . . . . . . . . 27
C.2. Address-scanning attacks . . . . . . . . . . . . . . . . . 27
C.3. Information Leakage . . . . . . . . . . . . . . . . . . . 28
C.4. Correlation of node activities within a network . . . . . 28
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction 1. Introduction
[RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for [RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for
IPv6 [RFC2460], which typically results in hosts configuring one or IPv6 [RFC2460], which typically results in hosts configuring one or
more "stable" addresses composed of a network prefix advertised by a more "stable" addresses composed of a network prefix advertised by a
local router, and an Interface Identifier (IID) that typically embeds local router, and an Interface Identifier (IID) that typically embeds
a hardware address (e.g., using IEEE identifiers) [RFC4291]. a hardware address (e.g., using IEEE identifiers) [RFC4291].
Cryptographically Generated Addresses (CGAs) [RFC3972] are yet Cryptographically Generated Addresses (CGAs) [RFC3972] are yet
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o embedding the underlying link-layer address in the Interface o embedding the underlying link-layer address in the Interface
Identifier leaks device-specific information that could be Identifier leaks device-specific information that could be
leveraged to launch device-specific attacks. leveraged to launch device-specific attacks.
o embedding the underlying link-layer address in the Interface o embedding the underlying link-layer address in the Interface
Identifier means that replacement of the underlying interface Identifier means that replacement of the underlying interface
hardware will result in a change of the IPv6 address(es) assigned hardware will result in a change of the IPv6 address(es) assigned
to that interface. to that interface.
Appendix B provides additional details regarding how these [I-D.cooper-6man-ipv6-address-generation-privacy] provides additional
vulnerabilities could be exploited, and the extent to which the details regarding how these vulnerabilities could be exploited, and
method discussed in this document mitigates them. the extent to which the method discussed in this document mitigates
them.
The "Privacy Extensions for Stateless Address Autoconfiguration in The "Privacy Extensions for Stateless Address Autoconfiguration in
IPv6" [RFC4941] (henceforth referred to as "temporary addresses") IPv6" [RFC4941] (henceforth referred to as "temporary addresses")
were introduced to complicate the task of eavesdroppers and other were introduced to complicate the task of eavesdroppers and other
information collectors (e.g. IPv6 addresses in web server logs or information collectors (e.g. IPv6 addresses in web server logs or
email headers, etc.) to correlate the activities of a node, and email headers, etc.) to correlate the activities of a node, and
basically result in temporary (and random) Interface Identifiers. basically result in temporary (and random) Interface Identifiers.
These temporary addresses are generated in addition to the These temporary addresses are generated in addition to the
traditional IPv6 addresses based on IEEE identifiers, with the traditional IPv6 addresses based on IEEE identifiers, with the
"temporary addresses" being employed for "outgoing communications", "temporary addresses" being employed for "outgoing communications",
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attacks, and that at the very least do not reveal the node's attacks, and that at the very least do not reveal the node's
identity when roaming from one network to another -- without identity when roaming from one network to another -- without
complicating the operation of the corresponding networks. complicating the operation of the corresponding networks.
However, even with "temporary addresses" in place, a number of issues However, even with "temporary addresses" in place, a number of issues
remain to be mitigated. Namely, remain to be mitigated. Namely,
o since "temporary addresses" [RFC4941] do not eliminate the use of o since "temporary addresses" [RFC4941] do not eliminate the use of
fixed identifiers for server-like functions, they only partially fixed identifiers for server-like functions, they only partially
mitigate host-tracking and activity correlation across networks mitigate host-tracking and activity correlation across networks
(see Appendix C.1 for some example attacks that are still possible (see [I-D.cooper-6man-ipv6-address-generation-privacy] for some
with temporary addresses). example attacks that are still possible with temporary addresses).
o since "temporary addresses" [RFC4941] do not replace the o since "temporary addresses" [RFC4941] do not replace the
traditional SLAAC addresses, an attacker can still leverage traditional SLAAC addresses, an attacker can still leverage
patterns in those addresses to greatly reduce the search space for patterns in those addresses to greatly reduce the search space for
"alive" nodes [Gont-DEEPSEC2011] [CPNI-IPv6] "alive" nodes [Gont-DEEPSEC2011] [CPNI-IPv6]
[I-D.ietf-opsec-ipv6-host-scanning]. [I-D.ietf-opsec-ipv6-host-scanning].
Hence, there is a motivation to improve the properties of "stable" Hence, there is a motivation to improve the properties of "stable"
addresses regardless of whether temporary addresses are employed or addresses regardless of whether temporary addresses are employed or
not. not.
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identifiers (as specified in [RFC2464]). It is meant to be identifiers (as specified in [RFC2464]). It is meant to be
employed for all of the stable (i.e. non-temporary) IPv6 addresses employed for all of the stable (i.e. non-temporary) IPv6 addresses
configured with SLAAC for a given interface, including global, configured with SLAAC for a given interface, including global,
link-local, and unique-local IPv6 addresses. link-local, and unique-local IPv6 addresses.
We note that of use of the algorithm specified in this document is We note that of use of the algorithm specified in this document is
(to a large extent) orthogonal to the use of "temporary addresses" (to a large extent) orthogonal to the use of "temporary addresses"
[RFC4941]. When employed along with "temporary addresses", the [RFC4941]. When employed along with "temporary addresses", the
method specified in this document will mitigate address-scanning method specified in this document will mitigate address-scanning
attacks and correlation of node activities across networks (see attacks and correlation of node activities across networks (see
Appendix C and [IAB-PRIVACY]). On the other hand, hosts that do not [I-D.cooper-6man-ipv6-address-generation-privacy] and [IAB-PRIVACY]).
implement/use "temporary addresses" but employ the method specified On the other hand, hosts that do not implement/use "temporary
in this document would, at the very least, mitigate the host-tracking addresses" but employ the method specified in this document would, at
and address scanning issues discussed in the previous section. the very least, mitigate the host-tracking and address scanning
issues discussed in the previous section.
3. Algorithm specification 3. Algorithm specification
IPv6 implementations conforming to this specification MUST generate IPv6 implementations conforming to this specification MUST generate
Interface Identifiers using the algorithm specified in this section Interface Identifiers using the algorithm specified in this section
in replacement of any other algorithms used for generating "stable" in replacement of any other algorithms used for generating "stable"
addresses (such as those specified in [RFC2464]). However, addresses with SLAAC (such as those specified in [RFC2464]).
implementations conforming to this specification MAY employ the However, implementations conforming to this specification MAY employ
algorithm specified in [RFC4941] to generate temporary addresses in the algorithm specified in [RFC4941] to generate temporary addresses
addition to the addresses generated with the algorithm specified in in addition to the addresses generated with the algorithm specified
this document. The method specified in this document MUST be in this document. The method specified in this document MUST be
employed for generating the Interface Identifiers for all the stable employed for generating the Interface Identifiers with SLAAC for all
addresses of a given interface, including IPv6 global, link-local, the stable addresses of a given interface, including IPv6 global,
and unique-local addresses. link-local, and unique-local addresses.
This means that this document does not formally obsolete or This means that this document does not formally obsolete or
deprecate any of the existing algorithms to generate Interface deprecate any of the existing algorithms to generate Interface
Identifiers (e.g. such as that specified in [RFC2464]). However, Identifiers (e.g. such as that specified in [RFC2464]). However,
those IPv6 implementations that employ this specification MUST those IPv6 implementations that employ this specification MUST
generate all of their "stable" addresses as specified in this generate all of their "stable" addresses as specified in this
document. document.
Implementations conforming to this specification SHOULD provide the Implementations conforming to this specification SHOULD provide the
means for a system administrator to enable or disable the use of this means for a system administrator to enable or disable the use of this
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Identifiers to be used with IPv6 Stateless Address Autoconfiguration Identifiers to be used with IPv6 Stateless Address Autoconfiguration
(SLAAC), as an alternative to e.g. Interface Identifiers that embed (SLAAC), as an alternative to e.g. Interface Identifiers that embed
IEEE identifiers (such as those specified in [RFC2464]). When IEEE identifiers (such as those specified in [RFC2464]). When
compared to such identifiers, the identifiers specified in this compared to such identifiers, the identifiers specified in this
document have a number of advantages: document have a number of advantages:
o They prevent trivial host-tracking, since when a host moves from o They prevent trivial host-tracking, since when a host moves from
one network to another the network prefix used for one network to another the network prefix used for
autoconfiguration and/or the Network ID (e.g., IEEE 802.11 SSID) autoconfiguration and/or the Network ID (e.g., IEEE 802.11 SSID)
will typically change, and hence the resulting Interface will typically change, and hence the resulting Interface
Identifier will also change (see Appendix C.1). Identifier will also change (see
[I-D.cooper-6man-ipv6-address-generation-privacy]).
o They mitigate address-scanning techniques which leverage o They mitigate address-scanning techniques which leverage
predictable Interface Identifiers (e.g., known Organizationally predictable Interface Identifiers (e.g., known Organizationally
Unique Identifiers) [I-D.ietf-opsec-ipv6-host-scanning]. Unique Identifiers) [I-D.ietf-opsec-ipv6-host-scanning].
o They may result in IPv6 addresses that are independent of the o They may result in IPv6 addresses that are independent of the
underlying hardware (i.e. the resulting IPv6 addresses do not underlying hardware (i.e. the resulting IPv6 addresses do not
change if a network interface card is replaced) if an appropriate change if a network interface card is replaced) if an appropriate
source for Net_Iface (Section 3) is employed. source for Net_Iface (Section 3) is employed.
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Interface Identifiers such as those specified in [RFC2464], but is Interface Identifiers such as those specified in [RFC2464], but is
not meant as an alternative to temporary Interface Identifiers (such not meant as an alternative to temporary Interface Identifiers (such
as those specified in [RFC4941]). Clearly, temporary addresses may as those specified in [RFC4941]). Clearly, temporary addresses may
help to mitigate the correlation of activities of a node within the help to mitigate the correlation of activities of a node within the
same network, and may also reduce the attack exposure window (since same network, and may also reduce the attack exposure window (since
temporary addresses are short-lived when compared to the addresses temporary addresses are short-lived when compared to the addresses
generated with the method specified in this document). We note that generated with the method specified in this document). We note that
implementation of this algorithm would still benefit those hosts implementation of this algorithm would still benefit those hosts
employing "temporary addresses", since it would mitigate host- employing "temporary addresses", since it would mitigate host-
tracking vectors still present when such addresses are used (see tracking vectors still present when such addresses are used (see
Appendix C.1), and would also mitigate address-scanning techniques [I-D.cooper-6man-ipv6-address-generation-privacy]), and would also
that leverage patterns in IPv6 addresses that embed IEEE identifiers. mitigate address-scanning techniques that leverage patterns in IPv6
addresses that embed IEEE identifiers.
Finally, we note that the method described in this document addresses Finally, we note that the method described in this document addresses
some of the privacy concerns arising from the use of IPv6 addresses some of the privacy concerns arising from the use of IPv6 addresses
that embed IEEE identifiers, without the use of temporary addresses, that embed IEEE identifiers, without the use of temporary addresses,
thus possibly offering an interesting trade-off for those scenarios thus possibly offering an interesting trade-off for those scenarios
in which the use of temporary addresses is not feasible. in which the use of temporary addresses is not feasible.
8. Acknowledgements 8. Acknowledgements
The algorithm specified in this document has been inspired by Steven The algorithm specified in this document has been inspired by Steven
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9.2. Informative References 9.2. Informative References
[RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks", [RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks",
RFC 1948, May 1996. RFC 1948, May 1996.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998. Networks", RFC 2464, December 1998.
[I-D.ietf-opsec-ipv6-host-scanning] [I-D.ietf-opsec-ipv6-host-scanning]
Gont, F. and T. Chown, "Network Reconnaissance in IPv6 Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", draft-ietf-opsec-ipv6-host-scanning-01 (work in Networks", draft-ietf-opsec-ipv6-host-scanning-02 (work in
progress), April 2013. progress), July 2013.
[I-D.ietf-v6ops-ra-guard-implementation] [I-D.ietf-v6ops-ra-guard-implementation]
Gont, F., "Implementation Advice for IPv6 Router Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", Advertisement Guard (RA-Guard)",
draft-ietf-v6ops-ra-guard-implementation-07 (work in draft-ietf-v6ops-ra-guard-implementation-07 (work in
progress), November 2012. progress), November 2012.
[I-D.cooper-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-cooper-6man-ipv6-address-generation-privacy-00 (work
in progress), July 2013.
[HDMoore] HD Moore, "The Wild West", Louisville, Kentucky, U.S.A. [HDMoore] HD Moore, "The Wild West", Louisville, Kentucky, U.S.A.
September 25-29, 2012, September 25-29, 2012,
<https://speakerdeck.com/hdm/derbycon-2012-the-wild-west>. <https://speakerdeck.com/hdm/derbycon-2012-the-wild-west>.
[Gont-DEEPSEC2011] [Gont-DEEPSEC2011]
Gont, "Results of a Security Assessment of the Internet Gont, "Results of a Security Assessment of the Internet
Protocol version 6 (IPv6)", DEEPSEC 2011 Conference, Protocol version 6 (IPv6)", DEEPSEC 2011 Conference,
Vienna, Austria, November 2011, <http:// Vienna, Austria, November 2011, <http://
www.si6networks.com/presentations/deepsec2011/ www.si6networks.com/presentations/deepsec2011/
fgont-deepsec2011-ipv6-security.pdf>. fgont-deepsec2011-ipv6-security.pdf>.
skipping to change at page 24, line 5 skipping to change at page 25, line 5
change upon replacement of the underlying network interface card). change upon replacement of the underlying network interface card).
A.4. Logical Network Service Identity A.4. Logical Network Service Identity
Host operating systems with a conception of logical network service Host operating systems with a conception of logical network service
identity, distinct from network interface identity or index, may keep identity, distinct from network interface identity or index, may keep
a Universally Unique Identifier (UUID) [RFC4122] or similar a Universally Unique Identifier (UUID) [RFC4122] or similar
identifier with the stability properties appropriate for use as the identifier with the stability properties appropriate for use as the
Net_Iface parameter. Net_Iface parameter.
Appendix B. Security/privacy issues with traditional SLAAC addresses
This section provides additional details regarding security/privacy
issues arising from traditional SLAAC addresses- Namely, it provides
additional details regarding how those issues could be exploited, and
the extent to which the method specified in this document mitigates
such issues.
B.1. Correlation of node activities within the same network
Since traditional SLAAC addresses employ Interface Identifiers that
are constant within the same network, such identifiers can be
leveraged to correlate the activities of a node within the same
network. One sample scenario is that in which a client repeatedly
connects to a server over a period of time, and hence, based on the
stable Interface Identifier, the server can correlate all
communication instances as being initiated by the same node.
The method specified in this document does not mitigate this attack
vector, since it produces Interface Identifiers that are constant
within a given network.
This attack vector could only be mitigated by employing "temporary
addresses" [RFC4941]. However, as noted in Appendix C.4, in
scenarios in which there is a reduced number of nodes in a given
network, mitigation of this vector might be difficult (if at all
possible) -- even with "temporary addresses" [RFC4941] in place.
B.2. Correlation of node activities across networks (host tracking)
Since traditional SLAAC addresses employ Interface Identifiers that
are constant across networks, such identifiers can be leveraged to
correlate the activities of a node across networks.
A passive version of this attack would be that in which a client
repeatedly connects to an attacker-operated server over a period of
time, and hence, based on the client's stable Interface Identifier,
the server can correlate all communication instances as being
initiated by the same node.
An attacker could also launch an active version of this attack. For
example, let us assume that the attacker knows the Interface
Identifier employed by the target node (e.g., the target and the
attacker were simultaneously connected to the same subnetwork at some
point in time). If the attacker knows the possible networks the
target might connect to, he could probe whether there is an address
with the target's Interface Identifier in each of those networks. If
such address is found to be "alive", then the attacker could infer
that the target node has connected to the corresponding network.
This vector is discussed in detail in Appendix C.1.2.
Since the method specified in this document results in Interface
Identifiers that are not constant across networks, both the passive
and active versions of this attack vector are mitigated.
B.3. Address-scanning attacks
Since traditional SLAAC addresses typically embed the underlying
link-layer address, the aforementioned addresses follow specific
patterns that can be leveraged to reduce the search space when
performing IPv6 address-scanning attacks (this is discussed in detail
in [I-D.ietf-opsec-ipv6-host-scanning]). The method specified in
this document produces random (but table within each subnet)
Interface Identifiers, thus mitigating this attack vector.
B.4. Exploitation of device-specific information
Since traditional SLAAC addresses typically embed the underlying
link-layer address, the aforementioned addresses leaks device-
specific information that might be leveraged to launch device-
specific attacks. For example, an attacker with knowledge about a
specific vulnerability in devices manufactured by some vendor might
easily identify potential targets by looking at the Interface
Identifier of a list of IPv6 addresses. The method specified in this
document produces random (but table within each subnet) Interface
Identifiers, thus mitigating this attack vector.
Appendix C. Privacy issues still present when temporary addresses are
employed
It is not unusual for people to assume or expect that all the
security/privacy implications of traditional SLAAC addresses are
mitigated when "temporary addresses" [RFC4941] are employed.
However, as noted in Section 1 of this document and [IAB-PRIVACY],
since temporary addresses are employed in addition to (rather than in
replacement of) traditional SLAAC addresses, many of the security/
privacy implications of traditional SLAAC addresses are not mitigated
by the use of temporary addresses.
This section discusses a (non-exhaustive) number of scenarios in
which host security/privacy is still negatively affected as a result
of employing Interface Identifiers that are constant across networks
(e.g., those resulting from embedding IEEE identifiers), even when
temporary addresses [RFC4941] are employed. It aims to clarify the
motivation of employing the method specified in this document in
replacement of the traditional SLAAC addresses even when privacy/
temporary addresses [RFC4941] are employed.
C.1. Host tracking
This section describes two attack scenarios which illustrate that
host-tracking may still be possible when privacy/temporary addresses
[RFC4941] are employed. These examples should remind us that one
should not disclose more than it is really needed for achieving a
specific goal (and an Interface Identifier that is constant across
different networks does exactly that: it discloses more information
than is needed for providing a stable address).
C.1.1. Tracking hosts across networks #1
A host configures its stable addresses with the constant Interface
Identifier, and runs any application that needs to perform a server-
like function (e.g. a peer-to-peer application). As a result of
that, an attacker/user participating in the same application (e.g.,
P2P) would learn the constant Interface Identifier used by the host
for that network interface.
Some time later, the same host moves to a completely different
network, and employs the same P2P application. The attacker now
interacts with the same host again, and hence can learn its newly-
configured stable address. Since the Interface Identifier is the
same as the one used before, the attacker can infer that it is
communicating with the same device as before.
C.1.2. Tracking hosts across networks #2
Once an attacker learns the constant Interface Identifier employed by
the victim host for its stable address, the attacker is able to
"probe" a network for the presence of such host at any given network.
See Appendix C.1.1 for just one example of how an attacker could
learn such value. Other examples include being able to share the
same network segment at some point in time (e.g. a conference
network or any public network), etc.
For example, if an attacker learns that in one network the victim
used the Interface Identifier 1111:2222:3333:4444 for its stable
addresses, then he could subsequently probe for the presence of such
device in the network 2011:db8::/64 by sending a probe packet (ICMPv6
Echo Request, or any other probe packet) to the address 2001:db8::
1111:2222:3333:4444.
C.1.3. Revealing the identity of devices performing server-like
functions
Some devices, such as storage devices, may typically perform server-
like functions and may be usually moved from one network to another.
Such devices are likely to simply disable (or not even implement)
privacy/temporary addresses [RFC4941]. If the aforementioned devices
employ Interface Identifiers that are constant across networks, it
would be trivial for an attacker to tell whether the same device is
being used across networks by simply looking at the Interface
Identifier. Clearly, performing server-like functions should not
imply that a device discloses its identity (i.e., that the attacker
can tell whether it is the same device providing some function in two
different networks, at two different points in time).
The scheme proposed in this document prevents such information
leakage by causing nodes to generate different Interface Identifiers
when moving from one network to another, thus mitigating this kind of
privacy attack.
C.2. Address-scanning attacks
While it is usually assumed that IPv6 address-scanning attacks are
unfeasible, an attacker can leverage address patterns in IPv6
addresses to greatly reduce the search space
[I-D.ietf-opsec-ipv6-host-scanning] [Gont-BRUCON2012]. Addresses
that embed IEEE identifiers result in one of such patterns that could
be leveraged to reduce the search space when other nodes employ the
same IEEE OUI (Organizationally Unique Identifier).
As noted earlier in this document, temporary addresses [RFC4941] do
not replace/eliminate the use of IPv6 addresses that embed IEEE
identifiers (they are employed in addition to those), and hence hosts
implementing [RFC4941] would still be vulnerable to address-scanning
attacks. The method specified in this document is meant as an
alternative to addresses that embed IEEE identifiers, and hence
eliminates such patterns (thus mitigating the aforementioned address-
scanning attacks).
C.3. Information Leakage
IPv6 addresses embedding IEEE identifiers leak information about the
device (Network Interface Card vendor, or even Operating System
and/or software type), which could be leveraged by an attacker with
device/software-specific vulnerabilities knowledge to quickly find
possible targets. Since temporary addresses do not replace the
traditional SLAAC addresses that typically embed IEEE identifiers,
employing temporary addresses does not eliminate this possible
information leakage.
C.4. Correlation of node activities within a network
In scenarios in which the number of nodes connected to a subnetwork
is small, preventing the correlation of the activities of those nodes
within such network might be difficult (if at all possible) to
achieve, even with temporary addresses [RFC4941] in place. As a
trivial example, consider a scenario where there is a single node (or
a reduced number of nodes) connected to a specific network. An
attacker could detect new addresses in use at that network along with
addresses that are no longer in use, and infer which addresses are
being employed by which hosts. This task is made particularly easier
by the fact that use of "temporary addresses" can be easily inferred
(since they follow different patterns from that of traditional SLAAC
addresses), and since they are re-generated periodically (i.e., after
a specific amount of time has elapsed).
Author's Address Author's Address
Fernando Gont Fernando Gont
SI6 Networks / UTN-FRH SI6 Networks / UTN-FRH
Evaristo Carriego 2644 Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706 Haedo, Provincia de Buenos Aires 1706
Argentina Argentina
Phone: +54 11 4650 8472 Phone: +54 11 4650 8472
Email: fgont@si6networks.com Email: fgont@si6networks.com
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