A tool to generate binary polyglots (files that are valid with several file formats).
Loosely named after Μιθραδάτης,
a famous polyglot.
Pronounced mɪtrə.
mitra.py file1.png file2.dcm gives you a working PNG/DICOM polyglot.
Check Corkami mini or tiny PoCs for input files. and the formats repository for some extra technical info.
It tries different layouts: Stacks (appended data), Cavities (blank space), Parasites (comments), Zippers (mutual comments).
It returns the offsets where the payloads 'switch sizes' for multi-ciphertexts.
Ex: Z(80-162-286)-DICOM^TIFF.be3b767b.dcm.tif is a DICOM/TIFF zipper
where the payloads switch side at offsets 0x80, 0x162 and 0x286.
The -s option extracts the 2 payloads separately, mixed with pseudo-random bytes
(it doesn't fix checksums afterwards).
Mitra doesn't generate crypto-polyglots or any polyglots with overlapping bytes, but it can definitely help to craft them.
The goal of this project was to explore polyglots layouts, formats abuses, and understand which format features enables which kind of abuse.
For example, in a chunk-based format, just find where to cut the file,
then wrap foreign data in a new chunk and insert the chunk.
So you just need to teach Mitra how to identify the type,
where to cut, and how to wrap.
You can prevent a software launch if you find a security risk, but a bad format design is not considered a risk in itself: it's just the parser's fault, not the designer's !
So if you review a bad file format, then maybe with Mitra you can quickly generate polyglots with many other formats and demonstrate the risks.
Delayed Magic at offset zero, No appended
Any offset Cavities start tolerated appended data data Footer
Z 7 A R P I D T P M A B B C C E E F F G G I I I I J J N O P L P P R R T B J P P W I X
i Z r A D S C A S P R M Z A P B L L l I Z C C D L P P E G S N E N I T I P a C C A D Z
p j R F O M R 4 P 2 B I M F V a F C O 3 D 2 G S G D K G F F F G v A A S 3
O L c v A F F a P P M v
2 N 1
Zip . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
7Z X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
Arj X X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
RAR X X X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
PDF X X X X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
ISO X X X X X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 40
DCM X X X X X X . X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 36
TAR X X X X X X . X X X X X X X X X X X X X X X X X X X X X X X 29
PS X X X X X X X X . 8
MP4 X X X X X X X X . 8
AR X X X X X X X X . 8
BMP X X X X X X X . 7
BZ2 X X X X X X X . 7
CAB X X X X X X X X . 8
CPIO X X X X X X X X . 8
EBML X X X X X X . 6
ELF X X X X X X X . 7
FLV X X X X X X X X . 8
Flac X X X X X X X X . 8
GIF X X X X X X X . 7
GZ X X X X X X X X . 8
ICC X X X X X X . 6
ICO X X X X X X X X . 8
ID3v2 X X X X X X X X . 8
ILDA X X X X X X X X . 8
JP2 X X X X X X X X . 8
JPG X X X X X X X X . 8
NES X X X X X X X . 7
OGG X X X X X X X X . 8
PSD X X X X X X X X . 8
LNK X X X X X X . 6
PE X X X X X X X . 7
PNG X X X X X X X X . 8
RIFF X X X X X X X X . 8
RTF X X X X X X X X . 8
TIFF X X X X X X X X . 8
BPG X X X X X X X X . 8
Java X X X X X X X . 7
PCAP X X X X X X X X . 8
PCAPN X X X X X X X X . 8
WASM X X X X X X X X . 8
ID3v1 . 0
XZ . 0
Formats combinations: 278
Notes that some formats are containers and apply to several file types.
Remarks and recommendations to design file formats
- Enforcing a magic at offset zero should be standard.
- Starting at offset zero and not enforcing a magic at zero is still exploitable (PS, MP4).
- Starting at any offset makes polyglots trivial.
- Enforcing a footer (like
XZ,ID3v1) is a great way to check if a file isn't truncated, and prevents 'naturally' appended data. - Most formats have a way to store parasite data, except very simple ones.
- Don't use a standard container in a non standard way. Use a different magic if you're only going to use similar structures to a limited extend.
Since these polyglots contain the magic signatures of both formats,
file may be able to detect them with the --keep-going arguments.
(it does not validate the formats, but at least gives you some information).
$ file --keep-going --raw "C(66)-PNG-DICOM.7e22f58e.dcm.png"
C(66)-PNG-DICOM.7e22f58e.dcm.png: PNG image data, 13 x 7, 1-bit colormap, non-interlaced
- DICOM medical imaging data
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