CSCD 434Network SecurityWinter 2013

Lecture 4BGP, DNS Vulnerabilities

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Overview

• Network Protocols are not secure– Not designed to be secure in first place

• Looked at TCP/IP – Spoofed packets, hijacked sessions, DoS

attacks and more

• Other Network Protocols – BGP and DNS– Attacks violate fundamental way

protocols work

Motivation

• Why do we try to protect protocols?– DNS must function– BGP ties the Internet together– Critical to functionality of global

communication– Entire world is dependent on correctly

functioning Internet– Critical infrastructure, Power grid, water,

Emergency systems, Banks, Transportation, medical, entertainment and WOW!!!

BGP Overview

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BGP Operations (Simplified)

Establish session on TCP port 179

Exchange all active routes

Exchange incremental updates

AS1

AS2

While connection is ALIVE exchangeroute UPDATE messages

BGP session

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Four Types of BGP Messages

• Open : Establish a peering session.

• Keep Alive : Handshake at regular intervals.

• Notification : Shuts down a peering session.

• Update : Announcing new routes or withdrawing previously announced routes.

announcement = prefix + attributes values

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ASPATH Attribute

AS7018135.207.0.0/16AS Path = 6341

AS 1239Sprint

AS 1755Ebone

AT&T

AS 3549Global Crossing

135.207.0.0/16AS Path = 7018 6341

135.207.0.0/16AS Path = 3549 7018 6341

AS 6341

135.207.0.0/16

AT&T Research

Prefix Originated

AS 12654RIPE NCCRIS project

AS 1129Global Access

135.207.0.0/16AS Path = 7018 6341

135.207.0.0/16AS Path = 1239 7018 6341

135.207.0.0/16AS Path = 1755 1239 7018 6341

135.207.0.0/16AS Path = 1129 1755 1239 7018 6341

More BGP Details

• Uses TCP as its transport protocol– This guarantees transport reliability– Eliminates complexity related to

designing reliability into protocol itself– BGP data enclosed within TCP packets

• Then, TCP used for acknowledgment, sequencing, and retransmission

• After setting up BGP session and exchanging initial routes, BGP peers trade incremental routing and notification updates

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Border Gateway Protocol

• Attacker Goals– Why attack BGP? What advantages?

Border Gateway Protocol

• Attacker Goals– Why attack BGP? What advantages?– Black Hole

• Drop traffic, make a prefix unreachable• Attract traffic to a router then drop it

– Redirection• Traffic flowing to a particular network forced

to take different path, may cause link to collapse

BGP • Why attack continued

–Subversion• Pass data through link to eavesdrop or

modify data

–Instability• Cause route dampening, connection outages

– Routes that change too frequently get penalized

Called “Route Flapping” leads to Route dampening - routes assigned a less

preferred status

• Cause increased BGP traffic and cause route convergence delays

BGP

• How to attack BGP?– Provide wrong information

• Connections that don't really exist• Reroute traffic through compromised routes• Provide contradictory or confusing

information

– Provide more frequent information• Advertise routes more often• Destabilize routing tables

– Example follows ...

YouTube Gets DoS’d

• Feb. 2008, Pakistan government bans YouTube - blasphemous content

• Nobody from Pakistan can get to YouTube• PCCW,

• One of the largest communications providers for Pakistan and China, was supposed to just block Pakistani users … Yet blocked all of their users from YouTube,

• Not just the Pakistani ones ...

YouTube Gets DoS’d

• Result ... all BGP speaking routers on the Internet believe Pakistan Telecom provides best connectivity to YouTube

• A complete denial of service (DoS),– Intentional or not!!!

BGP Routing Details• BGP rules state that longer routes are more

specific and preferred, more bits for network portion

• So, YouTube, owns IP space – 208.65.153.0/24, – 208.65.152.0/24 and – 208.65.154.0/23,

• YouTube announces single aggregated BGP route for

/24 prefixes, announced as 208.65.152.0/22

208.65.152.0/22 via AS 36561 (YouTube)

208.65.153.0/24 via AS 17557 (Pakistan Telecom)15

Review of Supernetting from CSCD330http://www.2000trainers.com/cisco-ccna-05/ccna-

classless-cidr-supernetting/

• Want to aggregate 8 network addresses between 131.0.0.0/16 and 131.7.0.0 /16

• So, range can now be designated as 131.0.0.0/13 This value aggregates all addresses between 131.0.0.1 and 131.7.255.254

Hijacked YouTube Visuals

• RIPE NCC has tools that monitor BGP routes– RIPE is regional Internet registry for

Europe, Middle East and Central Asia

• http://www.ripe.net/news/study-youtube-hijacking.html

• Actual animation of the entire event complete with music!!!!

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More BGP Problems

Similar BGP problem revealed atBlackhat 2008 • Anyone with a BGP router ...• ISPs, large corporations, governments,• Could intercept data headed to a target IP

address or group of addresses

• Attack intercepts only traffic headed to target addresses, not from them

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Blackhat 2008Tony" Kapela andAlex Pilosov

2008 Demo at Blackhat

• Tony Kapela and Alex Pilosov• Man-in-the-middle attack demonstrated at Defcon 2008

– Redirected traffic bound for Defcon to a system they controlled in New York and then routed it back to Las Vegas

– Good analysis of this attack athttp://blogs.techrepublic.com.com/networking/?p=663

2008 Demo at Blackhat

• What did they discover about BGP?• Pilosov's innovation

– Forward the intercepted data to actual destination, so that no outage occurs

– AS path prepending causes selected BGP routers to reject their deceptive advertisement

– Use these AS's to forward stolen data to its rightful recipients

– Using the way protocol is supposed to work to subvert it !!!

BGP MITM Attack

AS prepend for AS10

2008 Demo at Blackhat

• What could you do with this attack?• Corporate espionage,• Nation-state spying or • Intelligence agencies looking to mine Internet

data• Don't need cooperation of ISP's ...

BGP Vulnerabilities

• What vulnerabilities allow these types of attacks to happen?– Lack of authentication of BGP updates

• Are they coming from “trusted” routers?

– Updates sent in the clear– Updates themselves can be bogus

• By accident or deliberate can poison the routing tables

Memo on BGP Security Vulnerabilities Analysishttp://www.ietf.org/rfc/rfc4272.txt

BGP Fixes

• Countermeasures–TCP connection hijack protection

• MD5 hash signature• Insure that BGP messages have source address of legitimate peering BGP speaker

BGP Fixes

• Route Filtering– Used to enforce business relationships

between AS's– Create Access Control Lists (ACL's) of

prefixes for sending/receiving updates– Egress filters allow control of announced

routes to peers– Ingress filters check incoming routes for

validity• Make sure origin AS of route owns prefix

BGP Fixes

• Route Filtering continued– What's the Problem ?

• Hard to keep Internet routing registries current

• ISP's trust that their peer routers sending correct information

• Also, in practice filtering is against dynamic nature of Internet

• Policies change often, structure of AS's not tree

• AS's have multiple connections, difficult to apply strict filters

One Fix, SBGP

• SBGP – Secure BGP– Extension to BGP – Protect BGP from malicious or mistaken

updates– Adds authorization and authentication

• Attribute added to BGP updates to ensure updates valid

• Route messages secured with IPSec

– Based on PKI cryptographyhttp://www.net-tech.bbn.com/sbgp/sbgp-index.html

SBGP

• SBGP – Secure BGP– Adds Address Attestation (AA)

• Verify origin AS is authorized to advertise a particular address block

• Verify AS owns that address block

– Adds Route Attestation (RA)• Authorize neighbor AS's to propagate route

contained in an update

SBGP• SBGP

– More details• Uses PKI to authorize AA's and RA's• Private keys stored in S-BGP speakers• Public keys made available by hierarchical

PKI infrastructure

• Any problems with this?

Problems with SBGP

– Need to have hierarchical PKI in place and trusted by all ISP's

– Crytography intensive and part of huge overhead when BGP router reboots

– Routers may need large memory 20 MB to store public keys

– Routers can't always sign routes if routes have been aggregated

• Routes will have come from multiple sources

Problems with SBGP• Have prevented SBGP from being

deployed• Alternative methods have been suggested

– CISCO proposed soBGP – Secure Origin BGP– Lightweight alternative to SBGP– Uses existing trust relationships to validate

certificates - “Web of Trust”– IRV – Companion protocol to BGP

• Uses IRV servers, • Updates are verified by each AS IRV server in AS-

PATH

Domain Name System (DNS)

DNS Overview• Domain Name System

– Hierarchical system of name servers for resolving IP addresses to human readable names

www.yahoo.com from 209.131.36.158

– Designed in 1980's along with TCP/IP– Was and is implemented as open source

software• BIND – Berkeley Internet Name Domain

– Has had many discovered flaws– Current version is BIND version 9

Domain Name System

Hierarchical Name Space root

edunetorg ukcom ca

wisc ucb EWU cmu mit

cslabs

DNS Root Name Servers

Hierarchical service 13 Root name servers

for top-level domains Authoritative name

servers for subdomains

Specified when you register your domain

Local name resolvers contact authoritative servers when they do not know a name http://www.root-

servers.org/

DNS Lookup Example

ClientLocal DNS resolver

root & edu DNS server

EWU.edu DNS server

cslabs.ewu.edu

NS EWU.educslabs.ewu.edu

EWU.educslabs4.ewu.edu=IPaddr

cslabs.ewu.eduDNS serverYour Operating

System

Caching

DNS responses are cached Quick response for repeated queries

DNS negative queries are cached Save time for nonexistent sites, e.g.

misspelling

Cached data periodically times out Lifetime (TTL) of data controlled by owner of

data TTL passed with every record, must refresh if

expires

Lookup Using cached DNS Server

ClientLocal

DNS recursiveresolver

root & edu DNS server

ewu.edu DNS server

cslabs.ewu.eduDNS server

penguin.ewu.edu

penguin=IPaddr

penguin.ewu.edu

Domain Name System• Attacker Motivation• Why subvert DNS?

– Direct users to fraudulent web sites• Gain user information, banking and identity

– Do a DoS against a specific company – Direct users to iffy web sites

• Porn! Porn! Porn!

– China performs DNS cache poisoning as part of their content filtering - Great Firewall of China!!!

http://chinadigitaltimes.net/china/Internet-control/

DNS Attacks In General

• Several Attacks against DNS– Attack Bind software

• Overflow buffers to crash software• Escalate privilege, gain root access

– Intercept packets and change information• Inject wrong information into Nameserver

caches• Known as Cache poisoning ... more on this later

– Denial of Service against Nameservers• Self explanatory ...

DNS Attacks Rebinding• 2007 – Stanford Researchers discovered a flaw

in way DNS resolved by browsers• Scripts on web pages, can access another web site,

if same origin policy .. web browser security– Must have same domain, same protocol and

same hostname– Example: http://www.securebits.org:8080 and

http://www.securebits.org:8080/somefolder/ – Will be allowed but – http://www.securebits.org and

https://www.securebits.org will not be allowedReference for Same Origin Policy• http://www.w3.org/Security/wiki/

Same_Origin_Policy

DNS Attacks Rebinding• Stanford URL

http://crypto.stanford.edu/dns/

• Attacker exploits same origin policy as follows1. Builds website under his/her control,

Controls DNS server that resolves queries for that website

2. Victim accesses website for first time, DNS server gives out the correct IP address1. Later, attacker rebinds hostname of website with a false IP address1. Allows access into an internal network

DNS Attacks Rebinding• Ex.: Victim visits www.example.com

– Attacker's nameserver resolves it to65.54.43.32 (correct IP)• Victim downloads webpages including a script• A short TTL of the DNS record (2 secs) has been set• Requires victim's browser to access DNS again to

resolve www.example.com before running script• Now, www.example.com is rebound to 10.10.10.8

which is an internal IP address on victim's network, of a printer, router or other configurable device

• Attacker will have identified the IP ahead of time• Allows bypass of firewall to run script

DNS Attacks Rebinding• Results

– Can capture internal data, sensitive information on internal network machines of an enterprise

– Subverting typical way browser security is supposed to run by preventing scripts from executing from two separate domains

• Solutions– IP pinning - browser uses one IP address for

entire session in spite of the DNS record TTL– DNS resolvers

• Do not allow external names to resolve to internal addresses

Nice Reference for this Rebinding Attack

http://capec.mitre.org/data/definitions/275.html

DNS Attacks Cache Poisoning• DNS server generally serves the Domain’s own

customers

• Cache poisoning attack– Server does not correctly validate DNS responses

to have come from an authoritative source– Not required to !!!

– Attacker exploits flaw in DNS software that can

make it accept incorrect information– Server will end up caching incorrect entries

locally and later serve them to users

DNS Attacks Cache Poisoning• Slides courtesy of

http://www.networkworld.com/slideshows/2008/102008-dns-and-cache-poisoning.html?nwwpkg=nws

1.User inputs www.bigbank.com2. If domain isn't cached, server consults with Authoritative DNS server.3. Address cached and forwarded to end user, who is then connected.

DNS Attacks Cache Poisoning

1. Attacker figures out when a domain entry will expire on a caching server using readily available tools2. Attacker "races" legitimate DNS server, trying to get caching server to accept a fake response.3. In order to be accepted fake response must match query parameters of actual response

DNS Attacks Cache Poisoning

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1. Attacker gets DNS to accept fake response (matches query parameters): “www.bigbank.com Is at 6.7.8.9 (an address controlled by the attacker)”

2. DNS Server responds to user queries with fake address.

DNS Attacks Cache Poisoning

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Pharming

This kind of attack is often categorized as a pharming attack

• First, users think they are at a familiar site, but they aren't

• Unlike phishing where user spots a suspicious URL, this case URL is legitimate

• Browser resolves address of domain automatically

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Pharming Scale

• Scale of the Problem• Hundreds or even thousands of users can be

redirected if an attacker successfully inserts a single fake entry into a caching server

• Scale amplified by popularity of domain being requested– Maybe www.yahoo.com ….

• Even a moderately experienced hacker can cause a lot of trouble, obtaining passwords and other valuable information

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Pharming• DNS poisoning attacks have occurred

– January 2005, the domain name for a large New York ISP, Panix, was hijacked to a site in Australia

– In November 2004, Google and Amazon users were sent to Med Network Inc., an online pharmacy

– In March 2003, a group dubbed the "Freedom Cyber Force Militia" hijacked visitors to the Al-Jazeera Web site

• Presented them with the message "God Bless Our Troops"

Inherent DNS Vulnerabilities

• Users/hosts typically trust the host-address mapping provided by DNS

• No way for a host to authorize the use of its name for a given address

• No way to authenticate the entities providing the updated information

• Are they really nameservers?

• Text is sent in the clear – both request and reply

• Easy to eavesdrop or modify

DNS Defenses - DNSSEC http://www.dnssec-deployment.org/

• DNS Security (DNSSEC) to the rescue!• Adds data authentication and integrity

protection to DNS protocol• Inclusion of public keys and the use of

digital signatures to DNS information

• Not the complete answer• Are significant drawbacks to using

DNSSEC

Overview of DNSSEC• A zone administrator "digitally signs" a Resource

Record Set (RRSet)– Publishes this digital signature, along with zone

administrator's public key

– DNSSEC client can retrieve RRset digital signature, then check this signature using public key against locally calculated hash value of the RRset

– And, Validate zone administrator's public key to insure its a valid key

– If all these checks succeed ...

– Client has some confidence that DNS response was authentic

Requires Hierarchy of Trust• To start securely resolving DNSSEC,• Root key must be anchored in resolver at

your local computer or nameserver– Only when a resolver knows and trusts a

zone key can it validate the signatures belonging to that zone

• Because of chain of trust, a resolver has to carry only a few zone keys to be able to validate DNSSEC data on Internet

Problems DNSSEC

• Many Nameservers not running DNSSEC– Need to have most of them running it to be

valid

• Trust issues with keys and distributions of keys– PKI is complex and there are problems with

it for such a huge system as DNS• A lot of resistance to change when

fundamental protocol involved

Summary

• Common vulnerabilities for Internet protocols– Lack of authentication– Cleartext transmission of information– Can't protect integrity of information– Can't prevent Denial of Service

• Costs to implement fixes, is serious pushback from IPS's and vendors

• Right now, attacks will likely continue

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End

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