Saturday, 12 March 2016

IETF RFC 7707: Network Reconnaissance in IPv6 Networks

The IETF has just published RFC 7707, authored by Fernando Gont and Tim Chown. This RFC could probably be considered the "bible" of "IPv6 Network Reconnaissance", describing the state of the art in IPv6 Network Reconnaissance.

Besides its value in terms of analyzing a plethora of vectors for IPv6 network reconnaissance, this document has been valuable for triggering other work in the area of IPv6 addressing. Namely,

  • "Recommendation on Stable IPv6 Interface Identifiers" (draft-ietf-6man-default-iids)
  • "Security and Privacy Considerations for IPv6 Address Generation Mechanisms" (RFC 7721)
  • "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)" (RFC7217)

These efforts are in the process of formally updating IPv6 Stateless Address Autoconfiguration (SLAAC) in the hopes of mitigating a number of security and privacy issues arising from traditional IPv6 SLAAC (which typically embeds link-layer addresses in the Interface Identifiers), and has already led to changes in Linux implementation of SLAAC, thanks to the work of Hannes Frederic Sowa and others in NetworkManager and the Linux Kernel.

Enough said! -- Please take a look at RFC 7707.

Tuesday, 16 February 2016

Quiz: Weird IPv6 Traffic on the Local Network (updated with solution)

One thing that I enjoy a lot is capturing network traffic to subsequently try to figure out whether the captured traffic makes any sense -- you learn a lot that way.

The following packet was shared with me by Timo Hilbrink during the 10th Slovenian IPv6 Summit.

The quiz consists in explaining the packet trace bellow.

  • Apple iOS 8.3
  • Fritz!Box CPE

The "Crime Scene" (tcpdump packet trace):

Two packets:

19:00:02.246726 IP6 truncated-ip6 - 16011 bytes missing!(class 0x50, flowlabel 0x00040,
hlim 0, next-header unknown (64) payload length: 16035)
4006:a0bd:c0a8:b229:40e9:a79c:f129:50 > f141:8159::b002:ffff:32fc:0: ip-proto-64
19:00:02.252529 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 256)
fe80::be05:43ff:feea:be92 > ip6-allnodes: [icmp6 sum ok]
ICMP6, router
, length 256
hop limit 255, Flags [other stateful], pref high, router lifetime 1800s, reachable time
0s, retrans time 0s
prefix info option (3), length 32 (4): 4006:a0bd:c0a8:b229::/64, Flags [onlink, auto],
valid time 7200s, pref. time 0s
prefix info option (3), length 32 (4): 4006:11b:c0a8:b229::/64, Flags [onlink, auto],
valid time 6973s, pref. time 0s
prefix info option (3), length 32 (4): 4006:3e38:c0a8:b229::/64, Flags [onlink, auto],
valid time 6972s, pref. time 0s
prefix info option (3), length 32 (4): 2001:980:376d:1::/64, Flags [onlink, auto], valid
time 6603s, pref. time 3600s
rdnss option (25), length 24 (3): lifetime 1200s, addr: fd00::be05:43ff:feea:be92
mtu option (5), length 8 (1): 1500
unknown option (24), length 8 (1):
0x0000: 0008 0000 0708

So... can you explain what this packet trace is all about?


The solution to this quiz boils down to explaining the two packets in question.

Upon first inspection, the first packet looks like a malformed/corrupted IPv6 packet: the packet is truncated, has an IPv6 Source Address that does not really belong to the local subnet, and even has an unknown upper protocol (Next Header=64). Quite surprisingly, the second 32-bits of the IPv6 Source Address are c0a8:b229 which, if converted to decimal on a byte-by-byte basis, results in

Is this just a coincidence? -- Let's look at the first packet a bit closer, with Wireshark:

Looking at the packet decode, it's clear that while the Ethernet "Type" field is set to 0x86dd (IPv6), the IPv6 version field is actually set to version 4!

What we infer from this packet, is that the sending system (Apple iOS 8.3) fails to properly set the Ethernet Type field (i.e., bug #1). Hence, this IPv4 packet is identified at layer-2 as an IPv4 packet, and hence parsed as an IPv4 packet.

This is what the packet should look like (but doesn't):

Now.. what about the second packet? How and why is it actually generated?

First of all, it seems that the Fritz!Box CPE fails to perform a very simple sanity check: that the IP version field matches the protocol type identified by the Ethernet header. In this particular case, they do not patch, and the Fritz!Box CPE should have discarded the packet rather than process it (i.e., bug #2).

That said, the Fritz!Box CPE seems to detect that the sending system is sending packets from an incorrect IPv6 prefix, and hence sends a Router Advertisement message with a Prefix Information Option (PIO) that advertises the corresponding prefix with a preferred lifetime of 0 -- in the hopes that this prefix is "disabled" in the sending system. This seems to be some sort of feature of the Fritz!Box CPE that aims to mitigate e.g. misconfigurations. Obviously, in this particular case the RA sent by the Fritz!Box CPE will be of no use, since the sending system is not really employing the 4006:a0bd:c0a8:b229/64 prefix -- it is simply sending IPv4 packets with an incorrect Ethernet Type (0x86DD rather than 0x800).

So... what's the real IP packet that is being sent by Apple iOS 8.3? If we overwrite the incorrect EtherType of the first packet with 0x0800, and now decode the first packet again (such that it is decoded as an IPv4 packet rather than as an IPv6 packet), the output is:

19:00:02.246726 IP > Flags [S], seq 4047602009, win 65535, options [mss 1460,nop,wscale 5,nop,nop,TS val 1228667736 ecr 0,sackOK,eol], length 0

That is, the first packet of the packet trace was really an IPv4-based TCP SYN packet, which obviously looked like a malformed IPv6 packet when "incorrectly" decoded as an IPv6 packet.

Folks willing to take a closer look at the packet trace may find the corresponding pcap file here. The "corrected" pcap file (with the EtherType overwritten with 0x0800, such that the first packet is decoded as an IPv4 packet) can be found here.

  -- Fernando Gont

Friday, 5 February 2016

RFC7739: Security Implications of Predictable Fragment Identification Values

The IETF has published a new RFC by Fernando Gont: RFC7739.

This RFC analyzes the security and privacy implications of predictable Fragment Identification (ID) values, and proposes a number of algorithms that can be employed to select Fragment ID values such that the aforementioned issues are mitigated.

As a result of earlier (internet-draft) versions this document, a number of operating systems (ranging from Linux to Microsoft Windows) had patched their IPv6 implementations to mitigate the aforementioned issues.

Recent discussions at the IETF suggest that the upcoming revision of the core IPv6 specification will remove the suggestion to employ a global counter for the generation of IPv6 Fragment IDs.

Use of predictable identifiers have a long history in IETF protocols, as discussed in this recent internet-draft by Fernando Gont and Iván Arce.

Friday, 29 January 2016

New edition of "Hacking IPv6 Networks v3.0" (May 31 - June 2, 2016 - Stuttgart)

Fernando Gont will be teaching our renowned "Hacking IPv6 Networks v3.0" training course in Germany!

Date: May 31 - June 2, 2016
Place: Stuttgart, Germany

Learning Objectives:
This course will provide the attendee with in-depth knowledge of IPv6 security, such that the attendee is able to evaluate and mitigate the security implications of IPv6 in production environments.

The attendee will be given an in-depth explanation of each topic covered in this course, and will learn -- through hands-on exercises -- how each feature can be exploited for malicious purposes. Subsequently, the attendee will be presented with a number of alternatives to mitigate each of the identified vulnerabilities.

This course will employ a range of open-source tools to evaluate the security of IPv6 networks, and to reproduce a number of IPv6-based attacks. During the course, the attendee will perform a large number of exercises in a network laboratory (with the assistance of the trainer), such that the concepts and techniques learned during this course are reinforced with hands-on exercises. The attendee will be required to perform a large number of IPv6 attacks, and to envision mitigation techniques for the corresponding vulnerabilities.

More information about the training course, and online registration is available here.