5MMSSI information systems security Grenoble INP - Ensimag. 4 Network Security. Lecturers: Fabien Duchene, Karim Hossen

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1 5MMSSI information systems security Grenoble INP - Ensimag 4 Network Security Lecturers: Fabien Duchene, Karim Hossen

2 Summary Authentication Identity Authentication Password policies Identity federation Access control Principles Models Example 2 Perimeter security Firewall Proxy VPN IDS/IPS Network Access Control

3 4.1. Authentication 3 Identity Authentication Password policies Identity federation

4 Identification Identity: who are you? «Your identity is your most valuable possession. Protect it. And if anything goes wrong, use your powers!» Elastigirl The Incredibles 1 to n mapping 4

5 Authentication PROVE that you are who you claim to be 1 to 1 mapping Authentication factors: What I KNOW (eg: password) What I OWN (eg: OTP, smart card, smartphone) What I AM (eg: biometry) One authentication methods can rely on several factors! 5

6 Authentication factors - example One time password 6 Smart card

7 Authentication protocols (some) Applications Kerberos SSL Theorical: Zero knowledge proof 7

8 Authentication and security context Once authenticated, the entity gets: Tokens regarding its attributes Security groups Eg: on Active Directory Directory Services Each Security Principal (Computer, User, Security Group) owns: o an unique Security Identifier o is member of zero or more security group SID 8

9 Authentication and security context - SID SID example: (domain: CORP) User account SID 9 Group SIDs

10 Password policy Basic password policy example (Active Directory): 10

11 Identity federation Separating the authentication process ( Identity Provider ) and the access control one on the application ( Service provider ) Some implementations: Kerberos Single-Sign-On SAML (eg: SimpleSAML) MS ADFS Some IP examples: OpenID, Google, Facebook Some SP examples: Google, Facebook, your website? 11

12 Identity federation: the big picture Entities: User Service Provider Identity Provider U requests access to SP SP tells to authenticate to IP U authenticates to IP, which provide him a token U sends it to SP SP performs the access control and serves the client 12

13 MS Active Directory Federation Services 1 o Example in Business2Businness Web-Browser Single-Sign-On Corporation A (Authentication) Intranet 4 Identity Provider Corporation R (Ressource) DMZ FS-A - obtains the attributes from IP - build the claims (c1,c2) - add some information regarding C - signs them = SAML token [C,c1,c2]FS-A X.509 cert. exchange FS-R accepts FS-A tokens FS- A 3.2 HTTP 302 FS-A User authentication SAML Token Request 3 2 FS- Web- Proxy A 6 Token construction: - checks the FS-A token signature - and builds [C,c1,c2]FS-R FS- Web- Proxy R [C,c1,c2 ]FS-A FS-R ]. HTTP POST. A 2 c ain=,c1, m C 5 [ o d 7.1 rity u c se HTTP POST 2.1 Authenticate to FS-P B (HTTP 302). I need the claims c1,c2.. 1 Client C 13 DMZ Intranet HTTP GET / web app. B 8: HTTP 200 OK, servicing 8 Web Application Active Directory Federation Services 2.0 (2010), Philippe BERAUD, Microsoft

14 4.2. Access Control Access control principles Access control models MAC DAC R-BAC Windows ACL example 14

15 Access Control - definition Controlling which operations on which ressources are allowed to be performed by which entities Eg: Is Sophie allowed to perform the print operation on the printer IR2750C? Not only a matter of IT (eg: Building access control) At several OSI layers: File / application (eg: unix, allowed to execute such a file) Firewall: ip + port access control Eg: ethernet address access control 15

16 Access control main steps Setting up an access policy Relating resources and their control access Setting up an access controller implementing those informations Access Controller On windows implementations Security reference monitor Requester Human System Application 17 Requests the identity Target / ressource File Checks its Application Checks the rights Network port Monitors activity Network ressource...

17 Discretionary Access Control Based on requester identity Capability List o a ressource list and the associated rights for each requester.. Or by ACL - Access Control List Targets/ressources o A requester list and their rights per ressource Requesters ACL of the j ressource Rights of the requester i on the ressource j CL of the requester i

18 Mandatory Access Control Based on the resource sensibility (security label) the granted level of the requester AKA Bell-La Padula model No read-up No write-down 22

19 MAC example - Windows NT6+ Mandatory Integrity Levels: Object (could be a process) Processes System System 0x4000 Eg: WININIT.EXE Eg: kernel variables High 0x3000 Eg: Admin processes Medium 0x2000 Eg: OUTLOOK.EXE R R+W W Low 0x1000 Eg: IEXPLORE.EXE Untrusted High Medium Low R Untrusted 0x0000 Mandatory Access Control (Wikipedia) 23

20 Example Windows ACL Role-based access control Permissions do apply first from most GENERAL to most PRECISE scope (latest applied is more important) DENY preempts on ALLOW

21 Example Windows ACL Is Sophie allowed to? Print? Manage the printer? Manage documents? 25

22 4.3. Perimeter security Security at the network layers (transport & network) Part of the in-depth defense mechanism Traditional security view But Old, traditional mechanism This is NOT SUFICIENT today: a host protection is vital! Lack of flexibility, cost o Microsoft now pushes for a deperimeterization : IPSec boundaries 26

23 Firewall Introduction Firewall locations o Network edge o Endpoint & servers Packet filtering Stateful Packet Inspection Application firewalls Firewall policy Some stuff from Cyril Voisin s lecture: Base de la sécurité des réseaux", Principal Security Advisor, Microsoft 27

24 Firewall - introduction Filtering limits network access between at least two networks o 2 directions filtering o Rules, metrics o RFC2979 thus located between two networks o L2 switching capabilities o L3 router in an IP path Information Disclosure prevention: IPv4 network: Network Address Translation protects a network topology from being discovered o 1-to-1 mapping o 1-to-N mapping (discrimation regarding destination port) 28

25 Firewall introduction (2) Products Software firewall o Installable executable linux iptables Windows Advanced Firewall o Virtual machine Hardware accelerated firewall appliance = HW +SW o Eg: Juniper, NetASQ 29

26 Firewall locations Endpoint & servers host-based firewall Software: in-depth defense principle! Tight OS interactions (each socket or routing operation!) Easier to hack than separate firewalls DMZ (DeMilitarized Zone) "perimeter network" Picture source: Wikipedia Network Edge o Software o Virtualized o Hardware LAN 30 (controlled network) Firewall WAN (public network)

27 some common DMZ network topologies Two firewall levels the multiculture principle => different brands Internal network One firewall level: Internal network 31 Internet DMZ DMZ Internet

28 Stateless firewalls packet filtering 1st generation: o 1988 Dodong Sean James, Elohra (DEC) o Bill Cheswick and Steve Bellovin (AT&T Bell Labs) Filter packets for allowing some circuits: o Pass o Drop (silently discard) o Reject (error response to the sender) Depending of L3 (Network) and L4 (Transport) metrics o IP source/dest address o TCP/UDP source/dest port number Policy example: o allow TCP->21 traffic from networka to network B o deny all traffic from (any network) to (any network) 33 Upper layers (applicason, session, presentason ) Transport (UDP, TCP) Network (IP) Link (ethernet) Physical

29 Stateful packet inspection session filtering Attacks on 1st generation FW: o DoS: eg: SYN flood (firewall ressources consumption) 2rd generation o : Janardhan Sharma, Dave Presetto, and Kshitij Nigam o 1995: first commercial product by Nir Zuk s team (CheckPoint) Stores the connection state o is that new packet conform to that current connection? o or is it for a new connection? o see the NAT connection table (in your network lecture!) Additional conformance verification for: o TCP flags (SYN, ACK, RST, PSH, FIN) o Session state and the TCP sequence number! o If any packet does not correspond to the expected state, it is blocked! 34

30 Stateful firewalls TCP states 35

31 Stateful firewalls state table Statically limited size table Each entry: Source DesHnaHon port port Source IP DesHnaHon IP IP number Protocol Timeout (op$onnal) (op$onnal) (op$onnal) SMTP 35/50 Understanding the FW-1 State Table, Lance Spitzner Flushing policy: if the connection is closed, or if no packet is sent during the TIMEOUT time Some Internet Protocol numbers: IP number IP name 1 ICMP 6 TCP 17 UDP 36

32 SPI firewall - example Eg: web-server (HTTP on TCP 80) publishing over IPv4, protected by D-NAT (Destination NAT) in that case in 1-to-1 mapping Web Client 1 If any actor do not respect that, the packet will be dropped 7 37 SPI SourcePort: TCP S_Port: TCP D_Port: TCP 8082 S_IP: 87 D_IP: SYN S_Port: TCP 80 S_Port: TCP 8082 D_Port: TCP S_IP: D_IP: 87 6 SYN ACK 9 ACK D_Port: TCP S_IP: D_IP: 87 3 ACK 11 4 SYN processing 5 SYN ACK 10 Web-Server (listening on TCP 8082) Firewall SYN /28 DesSnaSonPort: TCP 80 SourceIP: DesSnaSonIP: Example: - TCP has a 3- way handshake (SYN, SYN ACK, ACK) - Public IP addresses. DMZ The client can now send its HTTP requests and the same kind of checks are performed during the WHOLE communication

33 Application firewalls 3nd generation o : Bill Cheswick (AT&T), Marcus Ranum, and Gene Spafford (Purdue) Has a protocol description o Sequences, data types & size : eg: HTTP, DNS QoS: traffic prioritization o Useful for applications with real-time requirements (eg: SIP) Upper layers (applicason, session, presentason ) Transport (UDP, TCP) Performs Deep Packet Inspection o blocks known attacks (exploit signature) ~ 80% viruses (signature too) o force specific protocol behavior eg: limiting the HTTP header to x bytes o blocks specific content Network (IP) Link (ethernet) Physical eg: sending PDF files via gmail 38 Bill Cheswick, The Design of a Secure Internet Gateway, USENIX 1990

34 Firewall policy Set of rules Example: Block all outgoing FTP traffic except from host to host Allow only a subset of commands of the SIP protocol Least privilege principle: The last evaluated rule has to be o Deny All traffic from any network to any network 41

35 Additional cool stuff Policy depending of the identity of authenticated users: Role-Based Access Control Could also have additional functions: Proxy Failover, Load-Balancing 42

36 Firewall - interlude 48 Firewalls and Internet security: repelling the wily hacker, William R. Cheswick, Steven M. Bellovin, Aviel D. Rubin

37 Proxy Acts as an intermediary for requests from clients to another service. Types Proxy Internet Forward Internal network Open Reverse Applications Internet Proxy Internet Proxy Internet Internal network Internal server (eg: webserver) o Squid o Microsoft Forefront Threat Management Gateway (ISA server) 49

38 Proxy - features Policy: Filtering at the application level o Similar to Deep-Packet Inspection eg: HTTP URL filtering DNS: blacklist Caching o Accelerating some requests o (eg: Forward proxy loading static content from google.fr from its cache rather than fetching it again from the Internet) Logging o Each corporation providing an internet access has to log requests (liability issues) the policy could be dependent of the authenticated user/comp. 52

39 Proxy - SOCKS SOCKet Security, RFC1928, default TCP port 1080 (server) The application has to "understand" a SOCKS dialog Eg: forward proxy in a corporation ; HTTP GET / allow HTTP, DNS from proxy to Internet Identity provider Client SOCKS HTTP Internal network TCP IP client- server SOCKS TCP IP client- proxy 53 Proxy Internet FW HTTP HTTP TCP TCP IP (source = proxy) IP (source = proxy/fw)

40 Virtual Private Network (VPN) Réseau Privé Virtuel Private (confidential) tunnel over a public network Interconnecting with remote office Connecting to the corporate network when outside Some protocols PPTP, L2TP/IPSec HTTPS SSH 54

41 Motivation: Cost reduction Use of an omnipresent infrastructure (the Internet) Risks the Internet can access inside the corporate network o strong authentication (at least 2 factors) o operational network teams, security teams 55

42 4.3. Conformité (conformance) Définition de modèles en fonction Du type de poste (client, serveur) Des besoins métiers (équipe) De la politique de sécurité Mise en pratique des modèles agents installés sur les postes clients et serveurs Alerte en cas de non-conformité (monitoring/audit) 56

43 IDS / IPS Intrusion Detection System: passif (enregistre, notifie) o Composant qui monitore le réseau et/ou le système o Reporte les comportements suspects ou violations de politiques Intrusion Prevention System: detects and reacts o Actions automatiques ou semi-automatiques Détection o Comportement statistiquement anormal (métriques?) o Signature (attack patterns) Problèmes Faux positifs: fausses alertes Faux négatifs: intrusions non détectées Position NIDS, NIPS: Network HIDS, HIPS: Host (server, client) 57

44 Antimalware Détection Classique: hash du binaire Heuristiques (intelligence artificielle) o Signature générique: Variations légères dans le code/binaire o Comportement (exécution en sandbox ou environnement virtualisé) Opérations (accès fichiers, configuration du système) Différences en environnement virtualisé ou non!! Détection non parfaite!! Cf théorie de Gödel sur l incomplétude et l incohérence. Problème INDECIDABLE Configuration Centralisée Selon des modèles de poste (KDC, serveur web ) o o o o Exclusions (que scanner? Processus, dossiers, ) Actions (autoriser, quarantaine, supprimer, demander) Mises à jour de définitions Scans complets du système Menaces: les antimalwares disposent de privilèges SYSTEM (iawacs 2010) 58

45 Antimalware - screenshots Exclusions Monitoring 59

46 XKCD interlude: voting machines & antimalware 60

47 Network Acces Control Poste client: Accès à certaines zones (capacité de communication avec certaines machines) en fonction: NON de la topologie du réseau Mais d un ensemble de métriques du poste client o Pare-feu activé? o Mises à jours installées? (antimalware, OS, applications ) o Chiffrement de la partition système? o Méthodes d isolation DHCP, 802.1X, VPN, IPSec Produits Cisco NAC Microsoft NAP (Protection) 61

48 4.3. Perimeter security - summary 62 Firewall Proxy VPN Conformance Statefull/stateless Which layers count for deciding? ApplicaSon Transport Network Do they perform masquerading? Eg NAT in IPv4 Deep- Packet InspecSon LocaSon: endpoint or network? QoS? Types Forward Open Reverse Features Filtering (DPI) Caching Logging (relasonship to authenscason) SOCKS L5 protocol Easier to administrate firewalls Cost reducson EncrypSon AuthenScaSon Could use symmetric or asymmetric crypto Evaluate the risks! Models for computers (server, client, team, use ) Intrusion DetecSon/ PrevenSon Sys Aiack models Undecidable problem AnSmalware Undecidable problem HeurisScs Network Access Control workstason metrics Different from topology segregason DHCP, 802.1X, IPSec

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