SKILL: Traffic Analysis & PCAP — Expert Analysis Playbook
AI LOAD INSTRUCTION: Expert traffic analysis and PCAP forensics techniques. Covers PCAP repair, Wireshark essential filters, protocol-specific analysis (HTTP, HTTPS/TLS, DNS, FTP, SMTP, USB HID, WiFi, ICMP), data extraction (file carving, credential harvesting, covert channels), NetworkMiner, and tshark CLI analysis. Base models miss USB keyboard decode patterns, DNS tunneling detection heuristics, and TLS decryption workflows.
0. RELATED ROUTING
Before going deep, consider loading:
- memory-forensics-volatility for correlating memory artifacts with network traffic
- steganography-techniques for analyzing files extracted from traffic captures
- network-protocol-attacks for understanding attack patterns visible in captures
- reverse-shell-techniques for identifying shell traffic in captures
1. PCAP REPAIR
bashpcapfix corrupted.pcap -o fixed.pcap # repair corrupted PCAP # Magic bytes: d4c3b2a1=pcap(LE), a1b2c3d4=pcap(BE), 0a0d0d0a=pcapng editcap -F pcap capture.pcapng capture.pcap # convert pcapng→pcap mergecap -w merged.pcap file1.pcap file2.pcap # merge captures
2. WIRESHARK ESSENTIAL FILTERS
IP / Host Filters
ip.addr == 10.0.0.1 # source or destination ip.src == 10.0.0.1 # source only ip.dst == 10.0.0.1 # destination only ip.addr == 10.0.0.0/24 # subnet !(ip.addr == 10.0.0.1) # exclude host
Protocol Filters
http # all HTTP dns # all DNS tcp # all TCP ftp # all FTP smtp # all SMTP tls # all TLS/SSL icmp # all ICMP arp # all ARP
TCP / Stream
tcp.stream eq 5 # follow specific TCP stream tcp.port == 80 # traffic on port 80 tcp.flags.syn == 1 && tcp.flags.ack == 0 # SYN packets (connection starts) tcp.analysis.retransmission # retransmitted packets tcp.len > 0 # packets with payload
HTTP
http.request.method == "POST" # POST requests http.request.method == "GET" # GET requests http.response.code == 200 # successful responses http.response.code >= 400 # error responses http.request.uri contains "login" # URI contains string http.host contains "target.com" # specific host http.content_type contains "json" # JSON responses http.cookie contains "session" # session cookies http.request.full_uri # show full URIs (column)
DNS
dns.qry.name contains "evil.com" # specific domain queries dns.qry.type == 1 # A records dns.qry.type == 28 # AAAA records dns.qry.type == 16 # TXT records dns.flags.response == 1 # DNS responses only dns.resp.len > 100 # large DNS responses
TLS
tls.handshake.type == 1 # Client Hello tls.handshake.type == 2 # Server Hello tls.handshake.extensions.server_name # SNI (hostname) tls.handshake.type == 11 # Certificate
Content Search
frame contains "password" # search in raw bytes frame contains "flag{" # CTF flag pattern tcp contains "admin" # search in TCP payload
3. PROTOCOL ANALYSIS
HTTP — Follow Stream & Extract
Right-click packet → Follow → TCP Stream # Shows full HTTP request/response conversation # File extraction: # File → Export Objects → HTTP → Save All # Useful filters for credential hunting: http.request.method == "POST" && frame contains "password" http.request.method == "POST" && frame contains "login" http.authbasic # Basic auth (base64 encoded)
HTTPS / TLS Decryption
bash# Method 1: SSLKEYLOGFILE (pre-master secrets from browser) # Set environment variable BEFORE opening browser: export SSLKEYLOGFILE=/tmp/sslkeys.log firefox https://target.com # Wireshark: Edit → Preferences → Protocols → TLS # → (Pre)-Master-Secret log filename: /tmp/sslkeys.log # Method 2: Server private key (for RSA key exchange only) # Wireshark: Edit → Preferences → Protocols → TLS → RSA keys list # → Add: IP, Port, Protocol, Key file (.pem)
DNS — Tunneling Detection
bash# Indicators of DNS tunneling: # 1. Unusually long subdomain names (>30 chars) # 2. High volume of TXT record queries/responses # 3. Consistent query patterns to same domain # 4. Base32/Base64-like subdomain strings # 5. High query frequency from single host # Wireshark filter for suspicious DNS: dns.qry.name.len > 50 # long query names dns.qry.type == 16 # TXT records (common for tunneling) dns.resp.len > 512 # large DNS responses # tshark extraction: tshark -r capture.pcap -Y "dns.qry.type==16" -T fields -e dns.qry.name
FTP — Credential & File Extraction
bash# FTP credentials (plaintext) # Filter: ftp.request.command == "USER" || ftp.request.command == "PASS" # FTP file transfer reconstruction: # FTP uses separate data channel (usually port 20 or dynamic) # Follow TCP stream of data connection to extract file # tshark: tshark -r capture.pcap -Y "ftp.request.command==USER || ftp.request.command==PASS" -T fields -e ftp.request.arg
SMTP — Email Content Extraction
bash# Follow TCP stream → MAIL FROM/RCPT TO/DATA sections # Attachments: base64 in MIME → decode Content-Transfer-Encoding blocks # Filters: smtp.req.command == "AUTH" # authentication (often base64) smtp contains "Content-Disposition: attachment" # attachments
USB — Keyboard HID Capture Decode
bash# USB HID keyboard traffic: interrupt transfers with 8-byte data # Filter: usb.transfer_type == 0x01 # Extract keystrokes: tshark -r usb.pcap -Y "usb.capdata && usb.data_len == 8" -T fields -e usb.capdata > keystrokes.txt # HID keycode layout: byte[0]=modifier, byte[2]=keycode # 0x04=a..0x1d=z, 0x1e=1..0x27=0, 0x28=Enter, 0x2c=Space # Use Python/online HID decoder to convert keycodes → text
WiFi — WPA Handshake
bash# Capture: airodump-ng --bssid AP_MAC -w capture wlan0mon # Convert + crack: hcxpcapngtool -o hash.hc22000 capture.pcap hashcat -m 22000 hash.hc22000 wordlist.txt # Deauth detection: wlan.fc.type_subtype == 0x0c
ICMP — Data Exfiltration
bash# ICMP payload analysis # Normal ping: 32 or 64 bytes of pattern data # Exfiltration: meaningful data in ICMP payload # Filter: icmp && data.len > 48 # unusual ICMP payload size icmp.type == 8 # echo requests # Extract ICMP payloads: tshark -r capture.pcap -Y "icmp.type==8" -T fields -e data.data
4. DATA EXTRACTION
File Carving
bash# Wireshark: File → Export Objects # Supported: HTTP, SMB, TFTP, IMF (email), DICOM # Manual from reassembled stream: # Follow TCP Stream → Show as Raw → Save As # binwalk on exported stream data binwalk -e exported_stream.bin foremost -i exported_stream.bin -o carved/
Credential Harvesting
bash# Plaintext: ftp || telnet || http.authbasic || smtp || pop || imap # NTLM: ntlmssp.auth.username → extract challenge/response from NTLMSSP messages # Hash format: user::domain:challenge:NTProofStr:blob → hashcat -m 5600
Covert Channel Detection
Indicators: DNS with long subdomains, ICMP with large payloads, HTTP with encoded headers, regular beacon intervals (C2). Use tshark -q -z io,stat,1 and -z conv,tcp for statistical anomaly detection.
5. NETWORKMINER
bash# Automated PCAP analysis: sudo apt install networkminer # Open PCAP → auto-extracts: Files, Images, Credentials, Sessions, DNS # Files tab: carved from HTTP/SMB/FTP | Credentials tab: plaintext creds
6. TSHARK COMMAND-LINE ANALYSIS
bashtshark -r capture.pcap -Y "http.request" -T fields -e http.host -e http.request.uri tshark -r capture.pcap -Y "dns.flags.response==0" -T fields -e dns.qry.name | sort -u tshark -r capture.pcap -Y "http.request.method==POST" -T fields -e http.file_data tshark -r capture.pcap -q -z io,stat,1 # I/O graph tshark -r capture.pcap -q -z conv,tcp # TCP conversations tshark -r capture.pcap -q -z endpoints,ip # IP endpoints tshark -r capture.pcap -q -z io,phs # protocol hierarchy tshark -r capture.pcap -q -z follow,tcp,ascii,0 # follow stream 0 tshark -r capture.pcap --export-objects http,/tmp/exported/
7. DECISION TREE
PCAP file for analysis │ ├── File won't open? │ ├── Check magic bytes: xxd | head (§1) │ ├── Repair: pcapfix (§1) │ └── Convert: editcap pcapng→pcap (§1) │ ├── What's in the capture? (Quick overview) │ ├── tshark -q -z io,phs (protocol hierarchy) (§6) │ ├── tshark -q -z conv,tcp (conversations) (§6) │ └── tshark -q -z endpoints,ip (endpoints) (§6) │ ├── HTTP traffic? │ ├── Export objects: File → Export Objects → HTTP (§4) │ ├── Credential hunt: POST + password/login filters (§3) │ ├── Follow streams: interesting request/response pairs (§3) │ └── Encrypted (HTTPS)? → need SSLKEYLOGFILE or RSA key (§3) │ ├── DNS traffic? │ ├── Long subdomains? → DNS tunneling (§3) │ ├── High TXT record volume? → DNS exfiltration (§3) │ ├── Extract all queries: tshark -Y dns -T fields -e dns.qry.name (§6) │ └── DNS rebinding? → check for alternating A record responses │ ├── FTP / Telnet / SMTP? │ ├── Extract credentials (plaintext) (§3) │ ├── Reconstruct file transfers (follow data stream) (§3) │ └── Email content and attachments (base64 decode) (§3) │ ├── USB traffic? │ ├── Keyboard HID → decode keystrokes (§3) │ ├── Storage → extract transferred files │ └── Check transfer_type and data_len fields │ ├── WiFi traffic? │ ├── WPA handshake → crack with hashcat (§3) │ ├── Deauth frames → detect attack (§3) │ └── Probe requests → device fingerprinting │ ├── ICMP traffic? │ ├── Large/variable payloads → data exfiltration (§3) │ ├── Regular pattern → ICMP tunnel (§3) │ └── Extract payloads: tshark -Y icmp -T fields -e data.data │ ├── Suspicious patterns? │ ├── Regular beacon interval → C2 communication (§4) │ ├── Unusual port/protocol combos → covert channel (§4) │ ├── High volume to single external IP → data exfil (§4) │ └── Encrypted traffic without SNI → suspicious tunnel │ └── Need automated extraction? ├── NetworkMiner for files/creds/images (§5) ├── tshark --export-objects for HTTP/SMB files (§6) └── binwalk/foremost on exported streams (§4)
