1. Network Infrastructure Insecurity
The authentication, management and routing protocols that run your network

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

3. The Network DMZ Internet Firewall Switch Router Host Host Host Host
Hub
Host
Printer
Radius Server

4. The Network DMZ Switch Router Host Host Host Host Hub Host Printer
Radius Server

5. The Network Switch Router Host Host Host Host Hub Host Printer
Radius Server

6. The Network
Switch
Router
Hub
Printer
Radius Server

7. Overview Network Infrastructure The building blocks of a network
basic network protocols
network management
authentication
routing
other random things
switches, hubs
printers
routers

8. 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

9. Overview
Impacts
Attacking protocols can allow for hijacking, spoofing and impersonation
control network devices
elevate access
change network flow
hide connections
sniffing
…and more

10. Basic Protocols Security at the IP layer discussed over and over
Security at the link layer ignored

11. 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.

12. ARP Security Flaws Lack of Authentication Limited Table Entries
ARP caches can be overpopulated and flushed

13. 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

14. 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.

15. 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.

16. 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”

17. DHCP Dynamic Host Configuration Protocol
Popular amongst pc users for ease of installation and configuration
UDP transport
To broadcast, from

18. DHCP Security Problems
Unauthenticated
Anyone can request an address
Undirected
Anyone can respond
Limited ACL capabilities
Limit addresses per mac

19. DHCP Attacks Get all addresses Deregister hosts Denial Of Service
Reply to requests with compromised host set as router or nameserver
Deregister hosts
hijack ip’s, connections

20. 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

21. Gateway Protocols
IGP
RIPv1
RIPv2
OSPF

22. 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.

23. RIP Security Flaws
Transport Method
Authentication

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

29. OSPF Security Flaws
Authentication

30. 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.

31. OSPF Attacks Forging OSPF messages
Can be somewhat difficult but theoretically possible if no authentication required or cleartext password obtained.

32. OSPF Solution
Enable MD5 Authentication in OSPF implementation.

33. 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

34. Authentication Mechanisms
Radius
TACACS, XTACACS, TACACS+
NIS/NIS+
LDAP

35. 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

36. 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)

37. 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( length user name attr + user pass attr + Secret)
Dictionary attack for Secret
radbrute.tar.gz

38. 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

39. 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

40. 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”

41. 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

42. TACACS+ TCP Transport Authentication and Encryption
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

43. TACACS+ ... Authentication Encryption 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

44. NIS and NIS+ Network Information Service Originally from Sun
Popular scheme for distributing password, name service, etc
RPC based transport

45. 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

46. NIS and NIS+ Solutions Run NIS+ if at all possible
Investigate alternatives like LDAP

47. LDAP Lightweight Directory Access Protocol
Operates on distinguished name (DN) and attribute pairs or collections

48. 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

49. Network Management and Other Fun Flaws
SNMP
printers

50. 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”

51. SNMPv1 Security Flaws Transport Mechanism Authentication
Data manipulation
Denial of Service
Replay
Authentication
Host Based
Community Based
Information Disclosure

52. SNMP Transport Mechanism Flaws
UDP Based
Unreliable - packets may or may not be received
Easily forged - trivial to forge source of packets

53. SNMP Authentication Flaws
Host Based
Fails due to UDP transport
DNS cache poisoning
Community Based
Cleartext community
Community name prediction/brute forcing
Default communities

54. 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...

55. SNMPv1 Information Disclosure
Routing tables
Network topology
Network traffic patterns
Filter rules

56. RMON and RMON2 Security SNMPv1’s flaws
additional hazards by introducing “action invocation” objects
collects extensive info on subnet
packet captures

57. SNMP Fixes
Disable it
ACL It
Read-Only

58. Printers Flaws Actually a very large potential problem
Laundering of hacking spoils
bounce attacks
Denial of service

59. 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

60. 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

61. Printer fixes?
Disable everything you can

62. 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

63. Examples Defeating things like SSH Gaining router access 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

64. 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?

65. 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

66. Questions?
Jeremy Rauch