OSPF Security Vulnerabilities Analysis

draft-ietf-rpsec-ospf-vuln-02.txt

emanuele.jones@alcatel.com

olivier.le_moigne@alcatel.com

IETF 66 – RPSEC Working GroupJuly 2006

Montreal, Canada

Draft’s overview

> Purpose• Provide a complete vulnerability analysis coverage for

OSPF• Leverage OSPF vulnerabilities assessment:

– Outline areas of intervention to harden the overall security of OSPF

– Provide a reference to better mandate requirements for security of future routing protocols

> Approach• systematic analysis of OSPF mechanisms and messages

to identify potential security vulnerabilities– General Vulnerabilities not tied to any specific OSPF message– Per-Message Vulnerabilities– Resource Consumption (DoS) Vulnerabilities

• not implementation specific• review of OSFP threats documents

Diff draft-ietf-rpsec-ospf-vuln-02.txt from 01

> Formatting: Nits have been fixed• document converted to xml to use xml2rfc• added missing sections (Security considerations)

Draft structure

> Definition of attacker and location• insider vs outsider• remote vs local

> Vulnerabilities• single intrusion, global impact

– one compromised router/link can impact all the stability of the network

• mechanism of “fight back”– information sent on behalf of another routers will be corrected– except in case of periodic inject where the attacker can induce

a permanent network state

• analysis message per message– malformed / malicious information– resource consumption

Examples of anomalies

> Neighborhood modification• Cryptographic Sequence Number Gap• Hello Replay• DR modification

> Rerouting by Modifying the Link State Database• MaxAge• Max Sequence Number• LSA Modification• Introduction of False External LSAs• Non-Existing Stub Networks

> Implementation Limits and Resources Consumption• Link State Database Overflow• Non-existing Links in Database Description• Multi Hellos Attack• Big Router LSA

> Other cases of IP Fragmentation> Malformed packets

Fight Back

> What is fight back?• Every LSA that is circulating containing wrong information

will be corrected by its owner

> Papers on OSPF security suggest that• Fight Back corrects the damage of most attacks • Many theoretical attacks are not worth the effort just to

cause a brief topology change

[ “An Experimental Study of Insider Attacks for the OSPF Routing Protocol”, Vetter et al.

“On the Vulnerabilities and Protection of OSPF Routing Protocol”, Wang and Wu ]

Example: Modifying a network topology

> Get an injection point• unprotected routing plane (no ACL, no authentication)

> Choose a LSA to modify

> Inject periodically (every second) the modify LSA with higher sequence numbers• The legitimate router will try to correct this but will fail:

“disabled fight back”

Next steps

> Finalize the draft

?

Back up slides

Three Examples from the Draft

> Three examples of vulnerabilities presented in the draft and how to exploit them :

Vulnerability Outcome ID’s Reference

LSA Modification Topology Changes 3.2.4.3-4

“Phantom” LSAs Database Overflow 3.3.5

External LSA Forwarding Data-Traffic Loop3.2.4.6

Exploit #1 – Topology Changes

> Vulnerability: LSA Information Modification [3.2.4.3-4]• Pre-condition:

– Being able to CONSTANTLY inject valid OSPF messages– Weak MD5 key choice/Compromised Router– No Cryptographic Authentication, etc…

• Possible Impact: Topology Changes– Allow Eavesdropping– Starve/Overload a network

• Expected Outcome: – Highly unstable topology (loops, route-flapping) due to Fight

Back of LSAs between attacker and legitimate owner

• Observed Outcome (as supported by the RFC!) – PERMANENT or SEMI-PERMANENT topology changes due to

ineffective Fight Back

Fight Back

> What is fight back?• Every LSA that is circulating containing wrong information

will be corrected by its owner

> Papers on OSPF security suggest that• Fight Back corrects the damage of most attacks • Many theoretical attacks are not worth the effort just to

cause a brief topology change

[ “An Experimental Study of Insider Attacks for the OSPF Routing Protocol”, Vetter et al.

“On the Vulnerabilities and Protection of OSPF Routing Protocol”, Wang and Wu ]

Disabling Fight Back

> OSPF Fight Back can be • Disabled • Heavily Diluted

> Attacks on LSA information are then SUCCESFUL

> HOW?1. Periodic Injection

> Exploiting an architectural “flaw” in the OSPF flooding algorithm > [ RFC 2328, 13.5 (a) (b) and (f) ]

> MinLSInterval (5 seconds)

2. Prevent information from reaching the router legitimate owner > Subverted router that partitions the network

3. Inject information on behalf of non-existing routers

Exploit #2 - Resource Consumption

> “Phantom LSAs” are Router/Network LSAs sent on behalf of non-existing OSPF peers

> These entries are ignored by the Shortest Path First (SPF) algorithm (do not produce topology changes)

> “Phantom LSAs” are entered in the Link State Database• Each entry is kept for MaxAge (1hour)• No fight back is triggered since there is no legitimate owner

> Exhausting Link-State Database resources will put OSPF in a very delicate state and stress implementation’s robustness

Exploit #3 - Creating a Data-Traffic Loop

> Vulnerability: Modifying External LSA Forwarding Field [3.2.4.6]• Pre-Condition:

– Being able to inject valid OSPF messages– Weak MD5 key choice/Compromised Router– No Cryptographic Authentication, etc…

– E-Bit Enabled on advertising peer’s Router LSA– Change Forwarding Address 0.0.0.0 to a router (host) in any Stub

Area

• Possible Impact:– Data never gets to its destination because it is stuck in a loop.– Outgoing External Traffic forwarded to a Stub Area router (host)

will LOOP between the ABR and its next hop towards the forwarding

point. [RFC 2328, 3.6]

Periodic Injection> When a legitimate owner receives a malicious copy of its own

LSAs:• SINCE

– the malicious LSA has higher sequence number– a copy of the LSA is already present in the LinkStateDB

and this copy was not received by flooding but installed by the router itself

• THEN Flood the malicious LSA and AFTER check ownership

• THEN TRY to update the malicious LSA [RFC 2328, 13, p.143-6]

• Why try?– Because a router cannot inject two same LSAs faster

than MinLSInterval (5 seconds) BUT it will immediately flood any LSA received. [RFC 2328, 12.4, p.125]

• If the attacker is injecting malicious LSAs with a rate higher than MinLSInterval, the legitimate owner will collaborate in the flooding

Data-Traffic Loop

Compromised RouterCompromised RouterCompromised RouterCompromised Router

123.1.2.0 123.1.2.0 E E123.1.2.0 123.1.2.0 E E............

F F E EF F E E

0.0.0.0 0.0.0.0 D D0.0.0.0 0.0.0.0 D D

D D direct directD D direct direct

F F direct directF F direct direct

0.0.0.0 0.0.0.0 E E0.0.0.0 0.0.0.0 E E

D D E ED D E E

F F direct directF F direct directFFFF

AAAA

BBBB

CCCC

EEEE

DDDD

GGGG

1111

2222

3333

BACKBONEBACKBONEBACKBONEBACKBONE

STUB AREASTUB AREASTUB AREASTUB AREA

123.1.2.0123.1.2.0123.1.2.0123.1.2.0 Ext. LSA 123.1.2.0 Forward Ext. LSA 123.1.2.0 Forward FF

is present in LinkStateDBis present in LinkStateDB

Ext. LSA 123.1.2.0 Forward Ext. LSA 123.1.2.0 Forward FF

is present in LinkStateDBis present in LinkStateDB

NO Ext. LSAs: 123.1.2.0 is NO Ext. LSAs: 123.1.2.0 is pointed to DEFAULT pointed to DEFAULT

ROUTEROUTE

NO Ext. LSAs: 123.1.2.0 is NO Ext. LSAs: 123.1.2.0 is pointed to DEFAULT pointed to DEFAULT

ROUTEROUTE

Attacker is advertising Attacker is advertising External Route to 123.1.2.0 External Route to 123.1.2.0

with Forward to Fwith Forward to F

Attacker is advertising Attacker is advertising External Route to 123.1.2.0 External Route to 123.1.2.0

with Forward to Fwith Forward to F

DATA TrafficDATA Traffic

TO: 123.1.2.0TO: 123.1.2.0

DATA TrafficDATA Traffic

TO: 123.1.2.0TO: 123.1.2.0

> An OSPF router could be attacked from ANYWHERE in the internet if the router’s IP address is known.

• Extremely easy to mount DDoS attacks for outsider attackers.• Extremely difficult to trace back the attacker

Attacker’s Location

Physical access to the linkPhysical access to the linkAttacker “On the Path”Attacker “On the Path”

Physical access to the linkPhysical access to the linkAttacker “On the Path”Attacker “On the Path”

Access to the link’s passwordAccess to the link’s passwordAccess to the link’s passwordAccess to the link’s passwordAccess to a routerAccess to a routerAccess to a routerAccess to a router

Telnet or SSH Telnet or SSH SessionSession

Telnet or SSH Telnet or SSH SessionSession

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFRouterRouterOSPFOSPF

RouterRouter

OSPFOSPFDomainDomainOSPFOSPF

DomainDomain

OSPFOSPFDomainDomainOSPFOSPF

DomainDomain

ATTACKERATTACKERATTACKERATTACKERATTACKERATTACKERATTACKERATTACKER ATTACKERATTACKERATTACKERATTACKER

INTERNETINTERNETINTERNETINTERNET

INTERNETINTERNETINTERNETINTERNET

Remote Attacker Backup

“The IP destination address for the packet is selected as follows. On physical point-to-point networks, the IP destination is always set to the address AllSPFRouters. On all other network types (including virtual links), the majority of OSPF packets are sent as unicasts, i.e., sent directly to the other end of the adjacency. In this case, the IP destination is just the Neighbor IP address associated with the other end of the adjacency (see Section 10).” RFC 2328, 8.1

Hop-by-hop OSPF’s Security

> All OSPF peers (on the same network) share the same secret key.

> If the attacker compromises ONE single link it can now attack the entire domain.• From the compromised link attacker can inject LSAs on

behalf of every other OSPF router (even if other links use a different secret!)

> Security Consequences: • Local Intrusion Global Impact

– Attacker that compromises one link/peer can possibly then attack anywhere in the entire domain

• Never know which is the compromised/malicious router– Even if an attack/suspicious behaviour is detected, it may not

be immediate to identify the malicious router

Stub-Area Default Route

“One or more of the stub area's area border routers must advertise a default route into the stub area via summary-LSAs. These summary defaults are flooded throughout the stub area, but no further.”

“These summary default routes will be used for any destination that is not explicitly reachable by an intra-area or inter-area path (i.e., AS external destinations).”

“An area can be configured as a stub when there is a single exit point from the area, or when the choice of exit point need not be made on a per-external-destination basis”

RFC 2328, 3.6, pag. 37

“Forwarding address Data traffic for the advertised destination will be forwarded to this address. If the Forwarding address is set to 0.0.0.0, data traffic will be forwarded instead to the LSA's originator (i.e., the responsible AS boundary router).”

RFC 2328, A.4.5, pag. 215