Jeremy Rauch <jrauch@securityfocus.com>

Network Infrastructure Insecurity

The authentication, management and routing protocols that run your

network

Topics

Overview Basic protocol flaws Network allocation flaws Routing protocol flaws Authentication flaws Network Management and other fun flaws Application of attacks

The Network

Router

Printer

Radius Server

Hub

Switch

DMZ

Internet

Host

Host

Host

Host

Host

Firewall

The Network

Router

Printer

Radius Server

Hub

Switch

DMZHost

Host

Host

Host

Host

The Network

Router

Printer

Radius Server

Hub

Switch

Host

Host

Host

Host

Host

The Network

Router

Printer

Radius Server

Hub

Switch

Overview

Network Infrastructure– The building blocks of a network

» basic network protocols

» network management

» authentication

» routing

» other random things switches, hubs printers routers

Overview

Does this stuff matter?– Absolutely - the network depends on these

» Basic protocols - obvious

» network management & allocation simplify network design and machine deployment

» Authentication access control

» Routing Getting from A to B

» Other stuff The network RUNS on these

Overview

Impacts– Attacking protocols can allow for hijacking,

spoofing and impersonation– control network devices– elevate access– change network flow– hide connections– sniffing– …and more

Basic Protocols

Security at the IP layer discussed over and over

Security at the link layer ignored

ARP

Address Resolution Protocol– Used for mapping network IP addresses to

physical (in the case of ethernet, MAC) interface addresses.

– Broadcast at the link layer.

ARP Security Flaws

Lack of Authentication Limited Table Entries

– ARP caches can be overpopulated and flushed

ARP Authentication Flaws

Lack of Authentication– Arp replies are typically accepted and cached

without concern for origin when received.

– No method to distinguish between legitimate and illegitimate messages

ARP Lack of Authentication

Invalid ARP replies– When an ARP who-is is broadcast on the wire,

anyone can reply and be mapped to the associated network address.

Gratuitous ARP replies– ARP replies without requests can be sent out and

cached, diverting traffic from the compromised network address to the attacker.

ARP Attacks

Replace entries in arp caches for existing addresses– Denial of Service

– Reply to requests with compromised host adress as router or nameserver.

– Non-blind traffic hijacking

– Exploitation of host-based trusts.

ARP Attacks

ARP Cache Overpopulation– Sending too many gratuitous ARP replies

flushing the target ARP cache in some implementations.

» Reach cache maximum, can cause devices like switches to re-enter “learning mode”

DHCP

Dynamic Host Configuration Protocol– Popular amongst pc users for ease of

installation and configuration– UDP transport– To broadcast, from 0.0.0.0

DHCP Security Problems

Unauthenticated– Anyone can request an address

Undirected– Anyone can respond

Limited ACL capabilities– Limit addresses per mac

DHCP Attacks

Get all addresses– Denial Of Service– Reply to requests with compromised host set as

router or nameserver Deregister hosts

– hijack ip’s, connections

DHCP Fixes

Authentication– ISC is adding authentication in their 3.1

implementation– Others have implemented proprietary

authentication mechanisms Don’t allow dynamic assignment of DNS

servers or routers– Statically define these

Gateway Protocols

IGP– RIPv1

– RIPv2

– OSPF

RIP

Routing Information Protocol– Widely used distance-vector IGP (Interior

Gateway Protocol) within autonomous systems.

– Exists in two forms, Version 1 and the backwards compatible Version 2.

RIPv1 is extremely vulnerable to serious attack.

RIP Security Flaws

Transport Method Authentication

RIP Transport Method Flaws

Based on UDP, utilizing port 520 for sending and receiving messages.– UDP is unreliable, no sequencing of packets.

Easy to send arbitrary data to target .

– Since sequencing is not a concern, forging source address can be very effective.

– May be able to receive data from anywhere on the internet.

RIP Authentication Flaws

Lack of any authentication in RIPv1 Cleartext Authentication recommended in

RFC 2453 RIPv2 Specifications MD5 Key/KeyID Digest Based

Authentication described in RFC 2082.

RIP Attacks

Forging RIP messages– Spoofing source address and sending invalid

routes, altering traffic flow.

» Traffic Hijacking

» Traffic Monitoring

» Redirecting traffic from trusted to untrusted.

– Obtaining Cleartext RIPv2 "password" when sent across network.

» Using retrieved password to send authenticated updates to RIPv2 routers, altering traffic flow with consequences listed above.

RIP Solutions

Disabling RIPv1 and using RIPv2 with MD5 authentication.

Enabling MD5 based authentication for RIPv2

Disabling RIP completely and using OSPF with MD5 authentication as interior gateway protocol. OSPF is the suggested IGP.

OSPF

OSPF - Open Shortest Path First– Link-State Interior Gateway Protocol. In wide

use within autonomous systems.

– OSPF is the recommended IGP, intended as a replacement for RIP.

OSPF Security Flaws

Authentication

OSPF Authentication Flaws

Default Lack of Authentication– By default in some implementations, OSPF

authentication may be off.

Cleartext "simple password" Authentication– Commonly a default setting, clear-text password

included in OSPF message used to authenticate peers.

Type of authentication determined by "CODE" field in the OSPF message header.

OSPF Attacks

Forging OSPF messages – Can be somewhat difficult but theoretically

possible if no authentication required or cleartext password obtained.

OSPF Solution

Enable MD5 Authentication in OSPF implementation.

Authentication Flaw Overview

Authentication is a means for verification and granting of access

Problems range from denial of service to active and passive attacks leading to total compromise– gain access– elevate access

Authentication Mechanisms

Radius TACACS, XTACACS, TACACS+ NIS/NIS+ LDAP

RADIUS

Remote Authentication Dial In User Service RFC 2138 & 2139 Used to authenticate users Off-machine/device authentication

– Central authentication server called a NAS– Popular implementations from Livingston and

Merit

Radius Security Model

UDP Based transport Each packet contains an authenticator

– Access-Requests» md5(secret + authenticator) ^ user password

– Access-Reject & Access-Accept» md5(Code + ID + Length + Request-Auth +

Attributes + Secret)

Radius Flaws

Gaining the shared secret– Send Access-Request with all known values

» Authenticator = 0

» User Name/Password = known

» Code = Access-Request (1)

» ID = 0, length = known

» Reply will come back with the following md5(1 + 0 + length + 0 + user name attr + user pass attr +

Secret)

» Dictionary attack for Secret radbrute.tar.gz

Radius Flaws...

Passive attack– Knowledge of a user password will allow attack

if sniffing is possible– Request-Access uses user password +

authenticator + shared secret» md5(authenticator + shared secret) ^ user pass

» obtain md5 by ^ userpass

» brute force dictionary attack with known authenticator

Radius Flaws...

Replay– Radius servers must not reuse authenticator

» if authenticator isn’t cryptographically random, repeat authentications until an authenticator is reused, and replay server Request-Accept

Failure limits and logging limit the effectivity

» Predictable authenticator If authenticator can be predicted, replay attacks become

easier and more effective

TACACS, XTACACS and TACACS+

Terminal Access Controller Access Control System??– Old protocol developed by BBN for Milnet

Similar in concept to RADIUS– Central authentication server moves

authentication off device or host RFC 1492, Internet Draft “The TACACS+

Protocol”

TACACS, etc Flaws

TACACS & XTACACS– UDP Transport

» spoof RESPONSE messages from server trivially

– Cleartext authentication normal» User names and password sent exposed

MD5 in newer implementations

– Good way to crack passwords online» Easy, fast way to grind for accounts with bad

passwords

TACACS+

TCP Transport– Doesn’t suffer from easy spoofing; may be

hijackable Authentication and Encryption

– May be possible to conduct attacks similar to RADIUS

Defaults and failure modes may pose problems– tacacs-server last-resort succeed

TACACS+ ...

Authentication– No integrity checking– Vulnerable to replay

Encryption– Heavy dependence on session id’s

» may be easy to force collision

» too small

– Lack of padding in critical places

NIS and NIS+

Network Information Service Originally from Sun Popular scheme for distributing password,

name service, etc RPC based transport

NIS and NIS+ Flaws

NIS transports in plaintext NIS is only protected by a domainname

– easily guessed Many vulnerabilities in implementations

– quick search for NIS and NIS+ vulnerabilities resulted in over a dozen individual problems

NIS+ is sufficiently complex to install that no one uses it

NIS and NIS+ Solutions

Run NIS+ if at all possible Investigate alternatives like LDAP

LDAP

Lightweight Directory Access Protocol Operates on distinguished name (DN) and

attribute pairs or collections

LDAP Flaws

New and relatively untested Unfamiliar Default ACL’s are typically poor Authentication mechanisms still not fully

implemented– CA based authentication still only part there

DoS attacks– Flood with requests

Network Management and Other Fun Flaws

SNMP printers

SNMP

Simple Network Management Protocol– The most popular network management

protocol– Hosts, firewalls, routers, switches…UPS,

power strips, ATM cards -- ubiquitous “One of the single biggest security

nightmares on networks today”

SNMPv1 Security Flaws

Transport Mechanism– Data manipulation– Denial of Service– Replay

Authentication– Host Based– Community Based

Information Disclosure

SNMPTransport Mechanism Flaws

UDP Based– Unreliable - packets may or may not be

received– Easily forged - trivial to forge source of

packets

SNMPAuthentication Flaws

Host Based– Fails due to UDP transport– DNS cache poisoning

Community Based– Cleartext community– Community name prediction/brute forcing– Default communities

SNMP Popular Defaults

Popular defaults– public

– private

– write

– “all private”

– monitor

– manager

– security

– admin

– lan

– default

– password

– tivoli

– openview

– community

– snmp

– snmpd

– system

– and on and on...

SNMPv1Information Disclosure

Routing tables Network topology Network traffic patterns Filter rules

RMON and RMON2Security

SNMPv1’s flaws additional hazards by introducing “action

invocation” objects collects extensive info on subnet packet captures

SNMP Fixes

Disable it ACL It Read-Only

Printers Flaws

Actually a very large potential problem Laundering of hacking spoils bounce attacks Denial of service

Printer flaws...

Many printers have FTP servers– Allow anonymous access

» store as much data as memory or disk space in the printer - great place to store hacking tools, sniffer logs, and other stolen things

– Most are poor implementations» easily used in more complex attacks

ftp bounce Berkeley lpd flaws

Printer flaws...

Denial of Service– Used as a tool to conduct DoS

» most love to respond to broadcast pings smurf

– Service denied» poor tcp/ip implementations

crash easily

» poor service implementation SNMP ftp

Printer fixes?

Disable everything you can

Example applications

Defeat sniffing– Race hosts on ARP replies– reply to ARP’s with broadcast address– overpopulate caches

» some switches will flush their caches

– alter routing on the host you want to sniff

Examples

Defeating things like SSH– Alter routing– Create SSH proxy

» Client will note key mismatch, but who ever pays attention?

Gaining router access– Obtain auth protocol key via brute force– Extract passwords on the wire– Just plain old sniff

What to do?

Maintain good perimeter defenses– At least you only have to trust your

employees… Use cryptographically secure transports

– Crypto is good» But crypto fails without good policy

Disable unneeded services– Not using SNMP?

What to do...

Disable things like routed on hosts– 99% of the time, static routes work fine on end

machines Use the strongest authentication methods

possible– Long keys, strong crypto

Questions?

Jeremy Rauch <jrauch@securityfocus.com>