cloudflare/filterforgeBPF 필터를 해결하고 이를 기반으로 패킷을 제작하기 위한 도구입니다.
Python 툴킷으로, Berkeley Packet Filter(BPF) 바이트코드를 역공학(reverse-engineering) 하기 위한 도구입니다. 맬웨어 샘플, 패킷 캡처 필터, 네트워크 장비에서 추출할 수 있는 원시 BPF 명령어를 입력받으면 filterforge가 이를 사람이 읽을 수 있는 형태로 디스어셈블하고, Z3를 사용하여 수용 경로를 만족하는 패킷 제약 조건 집합을 해결한 뒤, Scapy를 활용하여 해당 필터를 통과할 구체적인 네트워크 패킷을 생성합니다.
간단히 말해: BPF 프로그램을 넣으면 필터가 수용하는 완전한 형태의 패킷(Ethernet, IPv4/IPv6, TCP/UDP/SCTP 등)을 반환합니다 — 검사, PCAP 저장, 혹은 실제 네트워크 전송에 바로 사용할 수 있습니다.
이 도구를 실행하려면 uv를 설치하는 것이 좋습니다.
도구의 사용법에 대해서는 아래 예시를 참조하세요. 시간이 지남에 따라 더 많은 기능이 추가될 가능성이 있습니다.
주어진 BPF에 대해 빠르게 결과를 얻으려면 명령줄을 사용하는 것이 가장 쉽습니다. 일부 역공학 도구가 데이터를 복사된 형태로 반환하기 때문에, 원시 16진수 문자열 또는 16진수 값 배열을 제공할 수 있으며, -d 플래그를 사용하여 주어진 BPF의 디스어셈블리를 간단히 표시할 수 있습니다:
# 16진수 문자열
uv run ff -d -b "280000000c00000015002900060800001500000bdd860000300000001400000015000027110000002800000038000000150024003500000015002300e91400001500220043000000150021009c690000150020006c07000015001f0089000000280000003600000015001d0fe91400001500001d0008000030000000170000001500000f11000000280000001400000045001900ff1f0000b10000000e0000004800000010000000150015003500000015001400e91400001500130043000000150012009c690000150011006c0700001500100089000000480000000e00000015000e00e914000015000d009c69000015000c006c07000015000b0c890000001500000b06000000280000001400000045000900ff1f0000b10000000e000000500000001a000000740000000400000024000000040000000c000000000000000700000000000000400000000e000000150000012054454706000000000004000600000000000000"
# 16진수 값 배열
uv run ff -d -b "[0x28,0x0,0x0,0xc,0x15,0x0,0x1b,0x800,0x30,0x0,0x0,0x17,0x15,0x0,0x5,0x11,0x28,0x0,0x0,0x14,0x45,0x17,0x0,0x1fff,0xb1,0x0,0x0,0xe,0x48,0x0,0x0,0x16,0x15,0x13,0x14,0x7255,0x15,0x0,0x7,0x1,0x28,0x0,0x0,0x14,0x45,0x11,0x0,0x1fff,0xb1,0x0,0x0,0xe,0x48,0x0,0x0,0x16,0x15,0x0,0xe,0x7255,0x50,0x0,0x0,0xe,0x15,0xb,0xc,0x8,0x15,0x0,0xb,0x6,0x28,0x0,0x0,0x14,0x45,0x9,0x0,0x1fff,0xb1,0x0,0x0,0xe,0x50,0x0,0x0,0x1a,0x54,0x0,0x0,0xf0,0x74,0x0,0x0,0x2,0xc,0x0,0x0,0x0,0x7,0x0,0x0,0x0,0x48,0x0,0x0,0xe,0x15,0x0,0x1,0x5293,0x6,0x0,0x0,0xffff,0x6,0x0,0x0,0x0]"
주어진 BPF 바이트코드로부터 생성될 네트워크 패킷의 개요를 보려면 -c 플래그를 사용할 수 있습니다:
uv run ff -c -b "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"
2026-02-09 12:06:23,342 - INFO - Loaded 45 instructions
2026-02-09 12:06:23,342 - DEBUG - Found 50 accepting path(s)
2026-02-09 12:06:23,346 - DEBUG - Path 1 is satisfiable
2026-02-09 12:06:23,347 - INFO - Hexdump:
0000 00 00 00 00 00 00 00 00 00 00 00 00 86 DD 60 00 ..............`.
0010 00 00 00 00 84 00 00 00 00 00 00 00 00 00 00 00 ................
0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0030 00 00 00 00 00 00 D5 FA 00 00 00 00 00 00 00 00 ................
0040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
2026-02-09 12:06:23,347 - INFO - Packet summary:
###[ Ethernet ]###
dst = 00:00:00:00:00:00
src = 00:00:00:00:00:00
type = IPv6
###[ IPv6 ]###
version = 6
tc = 0
fl = 0
plen = 0
nh = SCTP
hlim = 0
src = ::
dst = ::
###[ SCTP ]###
sport = 54778
dport = 0
tag = 0x0
chksum = 0x0
###[ Raw ]###
load = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
일부 BPF는 원시 IP 계층을 사용할 수 있습니다. 이런 경우 링크 유형 -l raw를 지정할 수 있습니다 (기본값은 ethernet입니다);
uv run ff -c -b 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 -l raw
2026-02-09 12:06:46,064 - INFO - Loaded 229 instructions
2026-02-09 12:06:46,717 - DEBUG - Found 50 accepting path(s)
2026-02-09 12:06:46,725 - DEBUG - Path 1 unsatisfiable
2026-02-09 12:06:46,730 - DEBUG - Path 2 is satisfiable
2026-02-09 12:06:46,731 - INFO - Hexdump:
0000 45 00 00 00 00 00 00 00 00 11 00 00 00 00 00 00 E...............
0010 00 00 00 00 00 00 00 00 00 00 00 00 72 55 00 00 ............rU..
0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
2026-02-09 12:06:46,731 - INFO - Packet summary:
###[ IP ]###
version = 4
ihl = 5
tos = 0x0
len = 0
id = 0
flags =
frag = 0
ttl = 0
proto = udp
chksum = 0x0
src = 0.0.0.0
dst = 0.0.0.0
\options \
###[ UDP ]###
sport = 0
dport = 0
len = 0
chksum = 0x0
###[ Raw ]###
load = b'rU\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
도구를 프로그래밍 방식으로 사용하기 위해 비교적 사용하기 쉬운 API를 만들었습니다. 다양한 방식으로 구현할 수 있으며, 아래 예시를 참고하세요:
from ff import BPFSolver
# Create a solver with BPF bytecode
solver = BPFSolver("280000000c00000015001b00...")
# Solve and craft a packet
result = solver.solve()
if result:
result.hexdump()
result.show()
print(result.summary())
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
# Get human-readable disassembly
print(solver.disassemble())
# Access parsed instructions
print(f"Instruction count: {solver.instruction_count}")
for insn in solver.instructions:
print(insn)
from ff import BPFSolver, PacketOverrides
solver = BPFSolver("280000000c00000015001b00...")
# Override specific packet fields
overrides = PacketOverrides(
src_ip="192.168.1.100",
dst_ip="10.0.0.1",
src_port=12345,
dst_port=80,
src_mac="00:11:22:33:44:55",
dst_mac="aa:bb:cc:dd:ee:ff"
)
result = solver.solve(overrides=overrides)
if result:
result.show()
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
result = solver.solve()
if result:
# Save to PCAP file
solver.to_pcap("output.pcap")
# Or save a specific result
solver.to_pcap("output.pcap", result=result)
from ff import BPFSolver
# Use link_type="raw" for DLT_RAW (no Ethernet header)
solver = BPFSolver("280000000c00000015001b00...", link_type="raw")
result = solver.solve()
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
# Find all paths that lead to packet acceptance
paths = solver.find_paths()
print(f"Found {len(paths)} accepting path(s)")
for i, path in enumerate(paths):
print(f"Path {i+1}: {path}")
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
result = solver.solve()
if result:
# Raw bytes
raw_bytes = result.raw
# Scapy packet object for advanced manipulation
scapy_pkt = result.scapy_packet
scapy_pkt[0].dst = "192.168.1.1" # Modify directly
# Execution path taken
print(f"Path: {result.path}")
print(f"Link type: {result.link_type}")
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
result = solver.solve()
if result:
# Send packet (requires root/sudo)
solver.send(iface="eth0", count=1)
# Or send a specific result
solver.send(result=result, iface="eth0")
때때로 BPF에 예상되는 2개의 ret 명령어(패킷 수용용 1개, 패킷 드롭용 1개)가 없을 수 있습니다. 예를 들어 다음 Symbiote (dcfbd5054bb6ea61b8f5a352a482e0cf7e8c5545bd88915d3e67f7ba01c2b3d4) 예제를 보겠습니다:
uv run ff -d -b "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"
2026-02-09 12:08:32,009 - INFO - Loaded 44 instructions
(000) ldh [12]
(001) jeq #0x86dd, jt 2, jf 17
(002) ldb [20]
<SNIPPED>
(026) jeq #0xd5fa, jt 43, jf 27
(027) jeq #0xe5f6, jt 43, jf 28
(028) jeq #0xe912, jt 43, jf 29
(029) jeq #0xd65f, jt 43, jf 30
(030) jeq #0xe283, jt 43, jf 31
(031) jeq #0xfb42, jt 43, jf 32
(032) jeq #0xb26d, jt 43, jf 33
(033) jeq #0xf6fb, jt 43, jf 34
(034) ldh [x + 16]
(035) jeq #0xd5fa, jt 43, jf 36
(036) jeq #0xe5f6, jt 43, jf 37
(037) jeq #0xe912, jt 43, jf 38
(038) jeq #0xd65f, jt 43, jf 39
(039) jeq #0xe283, jt 43, jf 40
(040) jeq #0xfb42, jt 43, jf 41
(041) jeq #0xb26d, jt 43, jf 42
(042) jeq #0xf6fb, jt 43, jf 44
(043) ret #0 (DROP)
여기서 예상된 ret 명령어가 1개만 있음을 알 수 있습니다. 이로 인해 Z3 솔버가 실패합니다;
2025-12-16 12:09:31,123 - ERROR - No satisfiable paths found, failed to craft packet
BPF가 무엇을 하는지 살펴보면 성공적인 점프를 위해 자체 명령어를 추가할 수 있습니다. 위 스니펫에서 포트 번호와 관련된 조건이 매우 많음을 볼 수 있습니다. 각 조건은 다음 조건을 확인하거나 명령어 43으로 점프하는데, 이는 우리가 BPF를 디스어셈블하는 방식 때문에 DROP으로 표시됩니다. 이 경우 이것은 정확한 DROP이 아니라 유효한 반환문입니다. 따라서 자체 더미 성공 ret 명령어를 추가하면 올바르게 파싱됩니다. 예:
ret: 06 00 00 00 00 00 00 0006 00 00 00 ff ff 00 00 06 00 00 00 00 00 00 00결과:
uv run ff -d -b "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"
2025-12-16 12:12:04,346 - INFO - Loaded 45 instructions
(000) ldh [12]
(001) jeq #0x86dd, jt 2, jf 17
(002) ldb [20]
<SNIPPED>
(026) jeq #0xd5fa, jt 43, jf 27
(027) jeq #0xe5f6, jt 43, jf 28
(028) jeq #0xe912, jt 43, jf 29
(029) jeq #0xd65f, jt 43, jf 30
(030) jeq #0xe283, jt 43, jf 31
(031) jeq #0xfb42, jt 43, jf 32
(032) jeq #0xb26d, jt 43, jf 33
(033) jeq #0xf6fb, jt 43, jf 34
(034) ldh [x + 16]
(035) jeq #0xd5fa, jt 43, jf 36
(036) jeq #0xe5f6, jt 43, jf 37
(037) jeq #0xe912, jt 43, jf 38
(038) jeq #0xd65f, jt 43, jf 39
(039) jeq #0xe283, jt 43, jf 40
(040) jeq #0xfb42, jt 43, jf 41
(041) jeq #0xb26d, jt 43, jf 42
(042) jeq #0xf6fb, jt 43, jf 44
(043) ret #0xffff (ACCEPT)
(044) ret #0 (DROP)
이제 -c를 실행하여 패킷을 생성하면 새로운 마법 패킷이 나타납니다:
uv run ff -c -b "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"
2026-02-09 12:07:47,247 - INFO - Loaded 45 instructions
2026-02-09 12:07:47,247 - DEBUG - Found 50 accepting path(s)
2026-02-09 12:07:47,251 - DEBUG - Path 1 is satisfiable
2026-02-09 12:07:47,251 - INFO - Hexdump:
0000 00 00 00 00 00 00 00 00 00 00 00 00 86 DD 60 00 ..............`.
0010 00 00 00 00 84 00 00 00 00 00 00 00 00 00 00 00 ................
0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0030 00 00 00 00 00 00 D5 FA 00 00 00 00 00 00 00 00 ................
0040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
2026-02-09 12:07:47,252 - INFO - Packet summary:
###[ Ethernet ]###
dst = 00:00:00:00:00:00
src = 00:00:00:00:00:00
type = IPv6
###[ IPv6 ]###
version = 6
tc = 0
fl = 0
plen = 0
nh = SCTP
hlim = 0
src = ::
dst = ::
###[ SCTP ]###
sport = 54778
dport = 0
tag = 0x0
chksum = 0x0
###[ Raw ]###
load = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
로컬에서 테스트를 실행하려면:
uv run --extra dev pytest tests/ -v