CMPS122: COMPUTER SECURITY NETWORKING ATTACKS
NETWORKING ATTACKS NOTICES ▸ Lab #2 extended to Feb. 17 @ 23:59 ▸ HW #3 due tonight
NETWORKING ATTACKS LAST TIME ▸ TCP/IP networking stack ▸ Physical layer ▸ Data link layer ▸ Network layer ▸ Transport layer ▸ Application layer ▸ Concepts ▸ Protocols: an agreement on how to communicate ▸ “Dumb” network: Interior nodes have little knowledge of ongoing connections ▸ Layering: Layers depend on services from lower layer, and provide services to upper layer
NETWORKING ATTACKS TODAY ▸ Network attacks (Link, IP, and TCP layers) ▸ Wireshark demo
General Communication Security Goals: CIA • Confidentiality: – No one can read our data / communication unless we want them to • Integrity – No one can manipulate our data / processing / communication unless we want them to • Availability – We can access our data / conduct our processing / use our communication capabilities when we want to • Also: no additional traffic other than ours … 2 Slides based on David Wagner’s CS161
Link-layer threats • Confidentiality: eavesdropping (aka sniffing) • Integrity: injection of spoofed packets • Injection: delete legit packets (e.g., jamming) 3
Layers 1 & 2: General Threats? Framing and transmission of a collection of bits into individual messages sent across a 7 Application single � subnetwork � (one physical technology) 4 Transport 3 (Inter)Network 2 Link Encoding bits to send them over a single physical link 1 Physical e.g. patterns of voltage levels / photon intensities / RF modulation 4
Eavesdropping • For subnets using broadcast technologies (e.g., WiFi, some types of Ethernet), eavesdropping comes for � free � – Each attached system’s NIC (= Network Interface Card) can capture any communication on the subnet – Some handy tools for doing so o tcpdump / windump (low-level ASCII printout) o Wireshark (GUI for displaying 800+ protocols) 5
TCPDUMP: Packet Capture & ASCII Dumper 6
Wireshark: GUI for Packet Capture/Exam. 7
Wireshark: GUI for Packet Capture/Exam. 8
Wireshark: GUI for Packet Capture/Exam. 9
Stealing Photons 10
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Link-Layer Threat: Disruption • If attacker sees a packet he doesn’t like, he can jam it (integrity) • Attacker can also overwhelm link-layer signaling, e.g., jam WiFi’s RF (denial-of-service) 12
Link-Layer Threat: Disruption • If attacker sees a packet he doesn’t like, he can jam it (integrity) • Attacker can also overwhelm link-layer signaling, e.g., jam WiFi’s RF (denial-of-service) • There’s also the heavy-handed approach … 13
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Link-Layer Threat: Spoofing • Attacker can inject spoofed packets, and lie about the source address M D C Hello world! 15
Physical/Link-Layer Threats: Spoofing • With physical access to a local network, attacker can create any message they like – When with a bogus source address: spoofing • When using a typical computer, may require root/administrator to have full freedom • Particularly powerful when combined with eavesdropping – Because attacker can understand exact state of victim’s communication and craft their spoofed traffic to match it – Spoofing w/o eavesdropping = blind spoofing 16
On-path vs Off-path Spoofing Host A communicates with Host D Host C Host D Host A Router 1 Router 2 Router 3 On-path Router 5 Host B Host E Router 7 Router 6 Router 4 Off-path 17
Spoofing on the Internet • On-path attackers can see victim’s traffic ⇒ spoofing is easy • Off-path attackers can’t see victim’s traffic – They have to resort to blind spoofing – Often must guess/infer header values to succeed o We then care about work factor: how hard is this – But sometimes they can just brute force o E.g., 16-bit value: just try all 65,536 possibilities! • When we say an attacker � can spoof � , we usually mean � w/ reasonable chance of success � 18
Layer 3: General Threats? Bridges multiple � subnets � to 7 Application provide end-to-end internet 4 Transport connectivity between nodes 3 (Inter)Network 4-bit 8-bit 4-bit 2 Link 16-bit Total Length (Bytes) Header Type of Service Version Length (TOS) 1 Physical 3-bit 16-bit Identification 13-bit Fragment Offset Flags 8-bit Time to 8-bit Protocol 16-bit Header Checksum Live (TTL) 32-bit Source IP Address 32-bit Destination IP Address IP = Internet Protocol Payload 19
IP-Layer Threats • Can set arbitrary source address – � Spoofing � - receiver has no idea who you are – Could be blind, or could be coupled w/ sniffing – Note: many attacks require two-way communication o So successful off-path/blind spoofing might not suffice • Can set arbitrary destination address – Enables � scanning �� – brute force searching for hosts • Can send like crazy (flooding) – IP has no general mechanism for tracking overuse – IP has no general mechanism for tracking consent – Very hard to tell where a spoofed flood comes from! • If attacker can manipulate routing, can bring traffic to themselves for eavesdropping (not easy) 20
LAN Bootstrapping: DHCP • New host doesn’t have an IP address yet – So, host doesn’t know what source address to use • Host doesn’t know who to ask for an IP address – So, host doesn’t know what destination address to use • Solution: shout to � discover � server that can help – Broadcast a server-discovery message (layer 2) – Server(s) sends a reply offering an address ... host host host DHCP server 21
Dynamic Host Configuration Protocol D H C P d i s c o v e r ( b r o a d c a s t ) DHCP offer DHCP server new client � offer � message includes IP address, D H DNS server, � gateway C P r e q u e router � , and how long s t ( b r o a client can have these d c a s t ) ( � lease � time) DHCP ACK 22
Dynamic Host Configuration Protocol D H C P d i s c o v e r ( b r o a d c a s t ) DHCP offer DHCP server new client � offer � message includes IP address, D H DNS server, � gateway C P r e q u e router � , and how long s t ( b r o a client can have these d c a s t ) ( � lease � time) Threats? DHCP ACK 23
Dynamic Host Configuration Protocol D H C P d i s c o v e r ( b r o a d c a s t ) DHCP offer DHCP server new client � offer � message includes IP address, D H DNS server, � gateway C P r e q u e router � , and how long s t ( b r Attacker on same o a client can have these d c a s t ) subnet can hear ( � lease � time) new host’s DHCP request DHCP ACK 24
Dynamic Host Configuration Protocol D H C P d i s c o v e r ( b r o a d c a s t ) DHCP offer DHCP server new client � offer � message includes IP address, D H DNS server, � gateway C P r e q u e router � , and how long s t ( b r o a client can have these d c a s t ) ( � lease � time) DHCP ACK Attacker can race the actual server; if they win, replace DNS server and/or gateway router 25
DHCP Threats • Substitute a fake DNS server – Redirect any of a host’s lookups to a machine of attacker’s choice • Substitute a fake gateway router – Intercept all of a host’s off-subnet traffic o (even if not preceded by a DNS lookup) – Relay contents back and forth between host and remote server and modify however attacker chooses • An invisible Man In The Middle (MITM) – Victim host has no way of knowing it’s happening o (Can’t necessarily alarm on peculiarity of receiving multiple DHCP replies, since that can happen benignly) • How can we fix this? Hard 26
TCP 7 Application 4 Transport 3 (Inter)Network Source port Destination port 2 Link Sequence number 1 Physical Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data 27
TCP 7 Application These plus IP addresses define a given connection 4 Transport 3 (Inter)Network Source port Destination port 2 Link Sequence number 1 Physical Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data 28
TCP 7 Application Defines where this packet fits within the 4 Transport sender’s bytestream 3 (Inter)Network Source port Destination port 2 Link Sequence number 1 Physical Acknowledgment Advertised window HdrLen Flags 0 Checksum Urgent pointer Options (variable) Data 29
TCP Conn. Setup & Data Exchange Client (initiator) Server IP address 1.2.1.2, port 3344 IP address 9.8.7.6, port 80 SrcA=1.2.1.2, SrcP=3344, DstA=9.8.7.6, DstP=80, SYN, Seq = x 0 , 8 = c P r S 6 , 7 . + 1 . x . 8 = = 9 k A c c A S r y , = q S e K , C A + N S Y 4 , 4 3 3 = P s t D , . 2 . 1 2 1 . A = t s D SrcA=1.2.1.2, SrcP=3344, DstA=9.8.7.6, DstP=80, ACK, Seq = x+1, Ack = y+1 SrcA=1.2.1.2, SrcP=3344, DstA=9.8.7.6, DstP=80, ACK, Seq=x+1, Ack = y+1, Data= � GET /login.html 4 , 4 3 3 = P s t D , . 2 1 2 . 1 . = t A s D … � � 0 , 8 l > = m P h t r c < S … 6 , . K . 7 O . 8 0 = 9 0 A 2 c = � � S r a a t D , 1 6 + x = k c A 1 , + y = q e S K , C A 30
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