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Video-over-DNS TXT Records (sdomi.pl)

submitted 1 week ago by [email protected] to c/[email protected]

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It turns out you can get video over DNS TXT records. I saw “we made a globally distributed DNS network for shits and giggles” at 38c3. It can also be found on one of the presenter's webpage.

The presenter of “A Deep Dive into DNS” mentioned that some people have used TXT records to perform backups, so it was interesting to see that in action.

Obligitory bash warning: I added the --sandbox to sed and the “end of options” -- flag to the utilities that support it for security, but really, it depends on how much you trust mpv and the people who gave the talk I suppose, so be careful.

dig +short TXT {0..92}.vid.demo.servfail.network | sed --sandbox -- 's/[" ]*//g' | base64 -d -- | mpv -- -

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[–] [email protected] 4 points 1 week ago

Checks I Should Have Done Before Posting

Sorry for the self-posting. I just wanted to share my post-hoc file checks since it was due-diligence I didn't think of until after I shared.

TLDR: I redirected into a file and inspected it at least enough to say I received an mkv container with an h264 video and opus audio.

Caveats

I am not in any way knowledgeable about security.
You can do weird things with some files. I have no idea if mkv, opus, or h264 have comments or chimeras. See talks by Corkami for more information.
Quad9 uses a dynamic TXT record to let the user know if they have configured their DNS resolver correctly, so I imagine you could receive a different file than I did. I have included a SHA-512 checksum for convenience which only tells you anything if you trust me for some reason.

Details

I ran the command from my post in a world-readable directory with >mystery_video_file substituted for | mpv -- - and inspected the download with

sudo --user=nobody -- file -- mystery_video_file

which output

mystery_video_file: Matroska data

I ran rename --last -- '' '.mkv' mystery_video_file # the '' is the empty string delimited with apostrophes and then

sudo --user=nobody -- ffprobe -hide_banner -- mystery_video_file.mkv

which output

Input #0, matroska,webm, from 'mystery_video_file.mkv': Metadata: COMPATIBLE_BRANDS: isommp42 MAJOR_BRAND : mp42 MINOR_VERSION : 0 ENCODER : Lavf60.16.100 Duration: N/A, start: -0.007000, bitrate: N/A Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 256x144 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 1k tbn (default) Metadata: HANDLER_NAME : ISO Media file produced by Google Inc. Created on: 05/29/2024. VENDOR_ID : [0][0][0][0] ENCODER : Lavc60.31.102 libx264 Stream #0:1(eng): Audio: opus, 48000 Hz, stereo, fltp (default) Metadata: HANDLER_NAME : ISO Media file produced by Google Inc. Created on: 05/29/2024. VENDOR_ID : [0][0][0][0] ENCODER : Lavc60.31.102 libopus

If you trust me and not the presenter for some inexplicable reason, the SHA-512 checksum for the video is “24345bd3ca8015c14a7d5d63d6b2a40f9d0f8c0307a65996226a496f121fa5ae934718cf58090f43ee67bc250b06804f23c73688cc871c15c1ba18d79b1a82a8”.