cloudflare/filterforgeOutil de résolution de filtres BPF et de création de paquets basés sur ceux-ci.
Ensemble d'outils Python pour le rétro-ingénierie du bytecode Berkeley Packet Filter (BPF). Étant donné des instructions BPF brutes — celles que l'on pourrait extraire d'un échantillon de malware, d'un filtre de capture de paquets ou d'un équipement réseau — filterforge les désassemble sous forme lisible, utilise Z3 pour résoudre l'ensemble des contraintes de paquets qui satisfont un chemin acceptant, puis exploite Scapy pour forger un paquet réseau concret qui passerait le filtre.
En bref : donnez-lui un programme BPF et il vous rendra un paquet entièrement formé (Ethernet, IPv4/IPv6, TCP/UDP/SCTP et au-delà) que le filtre accepte — prêt à être inspecté, sauvegardé au format PCAP ou envoyé sur le réseau.
Il est recommandé d'installer uv pour exécuter cet outil.
Veuillez vous référer aux exemples ci-dessous pour l'utilisation de l'outil ; il est probable que davantage de fonctionnalités soient ajoutées au fil du temps.
Pour obtenir rapidement des résultats pour un BPF donné, il est plus simple d'utiliser la ligne de commande. En raison de la manière dont certains outils de rétro-ingénierie restituent les données copiées, vous pouvez soit donner une chaîne hexadécimale brute, soit un tableau de valeurs hexadécimales, en utilisant le drapeau -d pour simplement afficher le désassemblage du BPF donné ;
# chaîne hexadécimale
uv run ff -d -b "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"
# tableau de valeurs hexadécimales
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]"
Pour obtenir un aperçu de ce à quoi ressemblerait un paquet réseau s'il était fabriqué à partir du bytecode BPF donné, vous pouvez utiliser le drapeau -c :
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'
Certains BPF peuvent utiliser la couche IP brute ; vous pouvez spécifier le type de liaison -l raw à cet effet (par défaut ethernet) ;
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'
Pour une utilisation plus programmable de l'outil, nous avons créé une API relativement simple à utiliser, qui peut être implémentée de nombreuses manières différentes. Reportez-vous à certains des exemples ci-dessous pour vous inspirer :
from ff import BPFSolver
# Créer un solveur avec le bytecode BPF
solver = BPFSolver("280000000c00000015001b00...")
# Résoudre et fabriquer un paquet
resultat = solver.solve()
if resultat:
resultat.hexdump()
resultat.show()
print(resultat.summary())
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
# Obtenir un désassemblage lisible
print(solver.disassemble())
# Accéder aux instructions parsées
print(f"Nombre d'instructions : {solver.instruction_count}")
for insn in solver.instructions:
print(insn)
from ff import BPFSolver, PacketOverrides
solver = BPFSolver("280000000c00000015001b00...")
# Surcharger des champs spécifiques du paquet
surcharges = 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"
)
resultat = solver.solve(overrides=surcharges)
if resultat:
resultat.show()
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
resultat = solver.solve()
if resultat:
# Sauvegarder dans un fichier PCAP
solver.to_pcap("output.pcap")
# Ou sauvegarder un résultat spécifique
solver.to_pcap("output.pcap", result=resultat)
from ff import BPFSolver
# Utiliser link_type="raw" pour DLT_RAW (pas d'en-tête Ethernet)
solver = BPFSolver("280000000c00000015001b00...", link_type="raw")
resultat = solver.solve()
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
# Trouver tous les chemins qui mènent à l'acceptation du paquet
chemins = solver.find_paths()
print(f"{len(chemins)} chemin(s) acceptant(s) trouvé(s)")
for i, chemin in enumerate(chemins):
print(f"Chemin {i+1} : {chemin}")
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
resultat = solver.solve()
if resultat:
# Octets bruts
octets_bruts = resultat.raw
# Objet paquet Scapy pour manipulation avancée
pkt_scapy = resultat.scapy_packet
pkt_scapy[0].dst = "192.168.1.1" # Modifier directement
# Chemin d'exécution emprunté
print(f"Chemin : {resultat.path}")
print(f"Type de liaison : {resultat.link_type}")
from ff import BPFSolver
solver = BPFSolver("280000000c00000015001b00...")
resultat = solver.solve()
if resultat:
# Envoyer le paquet (nécessite root/sudo)
solver.send(iface="eth0", count=1)
# Ou envoyer un résultat spécifique
solver.send(result=resultat, iface="eth0")
Parfois, le BPF ne contient pas les 2 instructions ret attendues (1 pour accepter un paquet, 1 pour le rejeter). Prenons par exemple cet échantillon Symbiote (dcfbd5054bb6ea61b8f5a352a482e0cf7e8c5545bd88915d3e67f7ba01c2b3d4) :
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)
Nous pouvons voir ici que nous n'avons qu'une seule des instructions ret attendues, ce qui fait échouer notre solveur Z3 ;
2025-12-16 12:09:31,123 - ERROR - No satisfiable paths found, failed to craft packet
Nous pouvons ajouter notre propre instruction ici avec un saut réussi en regardant ce que fait le BPF. Dans l'extrait ci-dessus, on voit qu'il y a énormément de conditions liées aux numéros de port, chacune vérifiant soit la condition suivante, soit sautant à l'instruction 43, que nous notons comme DROP en raison de notre désassemblage du BPF. Dans ce cas, ce n'est pas exactement un DROP, mais une instruction de retour valide. Cela signifie que si nous ajoutons notre propre instruction ret de succès factice, elle sera parsée correctement, par exemple ;
ret actuel : 06 00 00 00 00 00 00 0006 00 00 00 ff ff 00 00 06 00 00 00 00 00 00 00Ce qui donne :
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)
Si nous exécutons maintenant notre -c pour fabriquer un paquet, nous serons accueillis par notre paquet magique tout neuf :
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'
Pour exécuter les tests localement :
uv run --extra dev pytest tests/ -v