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curbstickle_lw@lemmy.world

169

A sneaky demonstration of the dangers of curl bash (blog.k3can.us)

submitted 5 months ago* (last edited 5 months ago) by K3can@lemmy.radio to c/selfhosted@lemmy.world

65 comments fedilink hide all child comments

I set up a quick demonstration to show risks of curl|bash and how a bad-actor could potentially hide a malicious script that appears safe.

It's nothing new or groundbreaking, but I figure it never hurts to have another reminder.

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[–] deadbeef79000@lemmy.nz 7 points 5 months ago (2 children)

Does curl send a different useragent when it's piped?

Searching for those words just vomits 'hOW to SeT cUrL's UseRaGenT' blog spam.

[–] Flipper@feddit.org 20 points 5 months ago* (last edited 5 months ago) (1 children)

Its timing based. When piped a script, bash executes each line completly before taking the next line from the input. Curl has a limited output buffer.

Operation that takes a long time. Like a sleep, or if you want it less obvious. A download, an unzip operation, apt update, etc.
Fill the buffer with more bash commands.
Measure on the server if at some point curl stops downloading the script.
Serve a malicious payload.

[–] deadbeef79000@lemmy.nz 3 points 5 months ago

Oh that is clever.

[–] qupada@fedia.io 5 points 5 months ago

Not that I know of, which means I can only assume it'll be a timing-based attack.

With strategic use of sleep statements in the script you should stand a pretty good chance of detecting the HTTP download blocking while the script execution is paused.

If you were already shipping the kind of script that unpacks a binary payload from the tail end of the file and executes it, it's well within the realm of possibility to swap it for a different one.