Embed Size (px)
Citation preview
Jeremy Rauch <[email protected]>
Network Infrastructure InsecurityThe 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
HubSwitch
DMZ
Internet
Host
Host
Host
Host
Host
Firewall
The Network
Router
Printer
Radius Server
HubSwitch
DMZHost
Host
Host
Host
Host
The Network
Router
Printer
Radius Server
HubSwitch
Host
Host
Host
Host
Host
The Network
Router
Printer
Radius Server
HubSwitch
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
