anti
b1f6c3b84a
When ip_no_pmtu_disc=0 the Linux kernel sets DF=1 on TCP packets and uses IP ID=0 (RFC 6864). nmap's TI=Z fingerprint has no Windows match in its DB, causing 91% confidence guesses of 'Linux 2.4/2.6 embedded' regardless of TTL being 128. Setting ip_no_pmtu_disc=1 allows non-zero IP ID generation. Trade-off: DF bit is not set on outgoing packets (slightly wrong for Windows) but TI=Z is far more damaging to the spoof than losing DF accuracy.
100 lines
3.7 KiB
Python
100 lines
3.7 KiB
Python
"""
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OS TCP/IP fingerprint profiles for DECNET deckies.
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Maps an nmap OS family slug to a dict of Linux kernel sysctls that, when applied
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to a container's network namespace, make its TCP/IP stack behaviour resemble the
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claimed OS as closely as possible within the Linux kernel's constraints.
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All sysctls listed here are network-namespace-scoped and safe to set per-container
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without --privileged (beyond the NET_ADMIN capability already granted).
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Primary discriminator leveraged by nmap: net.ipv4.ip_default_ttl (TTL)
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Linux → 64
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Windows → 128
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BSD (FreeBSD/macOS)→ 64 (different TCP options, but same TTL as Linux)
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Embedded / network → 255
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Secondary discriminators (nmap OPS / WIN / ECN / T2–T6 probe groups):
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net.ipv4.tcp_syn_retries – SYN retransmits before giving up
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net.ipv4.tcp_timestamps – TCP timestamp option (OPS probes); Windows = off
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net.ipv4.tcp_window_scaling – Window scale option; embedded/Cisco typically off
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net.ipv4.tcp_sack – Selective ACK option; absent on most embedded stacks
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net.ipv4.tcp_ecn – ECN negotiation; Linux offers (2), Windows off (0)
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net.ipv4.ip_no_pmtu_disc – DF bit in ICMP replies (IE probes); embedded on
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net.ipv4.tcp_fin_timeout – FIN_WAIT_2 seconds (T2–T6 timing); Windows shorter
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Note: net.core.rmem_default is a global (non-namespaced) sysctl and cannot be
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set per-container without --privileged; TCP window size mangling is deferred to
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Phase 2 (iptables entrypoint).
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"""
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from __future__ import annotations
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OS_SYSCTLS: dict[str, dict[str, str]] = {
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"linux": {
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"net.ipv4.ip_default_ttl": "64",
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"net.ipv4.tcp_syn_retries": "6",
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"net.ipv4.tcp_timestamps": "1",
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"net.ipv4.tcp_window_scaling": "1",
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"net.ipv4.tcp_sack": "1",
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"net.ipv4.tcp_ecn": "2",
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"net.ipv4.ip_no_pmtu_disc": "0",
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"net.ipv4.tcp_fin_timeout": "60",
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},
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"windows": {
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"net.ipv4.ip_default_ttl": "128",
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"net.ipv4.tcp_syn_retries": "2",
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"net.ipv4.tcp_timestamps": "0",
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"net.ipv4.tcp_window_scaling": "1",
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"net.ipv4.tcp_sack": "1",
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"net.ipv4.tcp_ecn": "0",
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"net.ipv4.ip_no_pmtu_disc": "1", # avoid TI=Z: forces non-zero IP IDs
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"net.ipv4.tcp_fin_timeout": "30",
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},
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"bsd": {
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"net.ipv4.ip_default_ttl": "64",
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"net.ipv4.tcp_syn_retries": "6",
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"net.ipv4.tcp_timestamps": "1",
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"net.ipv4.tcp_window_scaling": "1",
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"net.ipv4.tcp_sack": "1",
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"net.ipv4.tcp_ecn": "0",
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"net.ipv4.ip_no_pmtu_disc": "0",
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"net.ipv4.tcp_fin_timeout": "60",
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},
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"embedded": {
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"net.ipv4.ip_default_ttl": "255",
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"net.ipv4.tcp_syn_retries": "3",
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"net.ipv4.tcp_timestamps": "0",
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"net.ipv4.tcp_window_scaling": "0",
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"net.ipv4.tcp_sack": "0",
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"net.ipv4.tcp_ecn": "0",
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"net.ipv4.ip_no_pmtu_disc": "1",
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"net.ipv4.tcp_fin_timeout": "15",
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},
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"cisco": {
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"net.ipv4.ip_default_ttl": "255",
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"net.ipv4.tcp_syn_retries": "2",
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"net.ipv4.tcp_timestamps": "0",
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"net.ipv4.tcp_window_scaling": "0",
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"net.ipv4.tcp_sack": "0",
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"net.ipv4.tcp_ecn": "0",
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"net.ipv4.ip_no_pmtu_disc": "1",
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"net.ipv4.tcp_fin_timeout": "15",
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},
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}
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_DEFAULT_OS = "linux"
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_REQUIRED_SYSCTLS: frozenset[str] = frozenset(OS_SYSCTLS["linux"].keys())
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def get_os_sysctls(nmap_os: str) -> dict[str, str]:
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"""Return the sysctl dict for *nmap_os*. Falls back to Linux on unknown slugs."""
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return dict(OS_SYSCTLS.get(nmap_os, OS_SYSCTLS[_DEFAULT_OS]))
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def all_os_families() -> list[str]:
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"""Return all registered nmap OS family slugs."""
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return list(OS_SYSCTLS.keys())
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