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https://github.com/corkami/pocs
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Ange Albertini
110 lines
2.4 KiB
Python
110 lines
2.4 KiB
Python
#!/usr/bin/env python
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# script to collide "MP4"-based files with specific `ftyp`
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# Ange Albertini, December 2019
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import struct
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import sys
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import hashlib
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def dprint(s):
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DEBUG = True
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DEBUG = False
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if DEBUG:
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print("D " + s)
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def relocate(d, delta):
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# finds and relocates all Sample Tables Chunk Offset tables
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# TODO: support 64 bits `co64` tables ()
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offset = 0
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tablecount = d.count("stco")
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dprint("stco found: %i" % tablecount)
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for i in range(tablecount):
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offset = d.find("stco", offset)
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dprint("current offset: %0X" % offset)
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length = struct.unpack(">I", d[offset-4:offset])[0]
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verflag = struct.unpack(">I", d[offset+4:offset+8])[0]
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offcount = struct.unpack(">I", d[offset+8:offset+12])[0]
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if verflag != 0:
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dprint(" version/flag not 0 (found %X) at offset: %0X" % (verflag, offset+4))
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continue
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# length, type, verflag, count - all 32b
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if (offcount + 4) * 4 != length:
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dprint(" Atom length (%X) and offset count (%X) don't match" % (length, offcount))
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continue
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dprint(" offset count: %i" % offcount)
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offset += 4 * 3
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offsets = struct.unpack(">%iI" % offcount, d[offset:offset + offcount * 4])
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dprint(" offsets (old): %s" % `list(offsets)`)
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offsets = [i + delta for i in offsets]
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dprint(" (new) offsets: %s" % `offsets`)
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d = d[:offset] + struct.pack(">%iI" % offcount, *offsets) + d[offset+offcount*4:]
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offset += 4 * offcount
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dprint("")
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return d
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def freeAtom(l):
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return struct.pack(">I", l) + "free" + "\0" * (l - 8)
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def isValid(d):
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# fragile check of validity
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return d.startswith("\0\0\0") and d[:32].count("ftyp") > 0
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fn1, fn2 = sys.argv[1:3]
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with open(fn1, "rb") as f:
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d1 = f.read()
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with open(fn2, "rb") as f:
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d2 = f.read()
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assert isValid(d1)
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assert isValid(d2)
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d1 = d1[0x20:]
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d2 = d2[0x20:]
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l1 = len(d1)
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l2 = len(d2)
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suffix = "".join([
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struct.pack(">I", 0x100 + 8), "free",
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"\0" * (0x100 - 8),
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struct.pack(">I", 8 + l1), "free",
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relocate(d1, 0x1C0 + 8 - 0x20),
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relocate(d2, 0x1C0 + 8 - 0x20 + l1),
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])
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# 32b length prefix
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with open("mp4s1.bin", "rb") as f:
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prefix1 = f.read()
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with open("mp4s2.bin", "rb") as f:
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prefix2 = f.read()
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col1 = prefix1 + suffix
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col2 = prefix2 + suffix
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md5 = hashlib.md5(col1).hexdigest()
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if md5 == hashlib.md5(col2).hexdigest():
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print "common md5: %s" % md5
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with open("collisions1.mp4", "wb") as f:
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f.write(col1)
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with open("collisions2.mp4", "wb") as f:
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f.write(col2)
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