this post was submitted on 29 Sep 2024
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The CUPS explout is here: GitHub - RickdeJager/cupshax (github.com)
submitted 1 month ago by [email protected] to c/linux
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cross-posted from: https://lemmy.zip/post/23601247

I hope this goes without saying but please do not run this on machines you don't own.

The good news:

  • the exploit seems to require user action

The bad news:

  • Device Firewalls are ineffective against this

  • if someone created a malicious printer on a local network like a library they could create serious issues

  • it is hard to patch without breaking printing

  • it is very easy to create printers that look legit

  • even if you don't hit print the cups user agent can reveal lots of information. This may be blocked at the Firewall

TLDR: you should be careful hitting print

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[–] [email protected] 15 points 1 month ago (1 children)

As other articles pointed out, this is only a problem if:

  • You expose port 631 to the internet.
    • Why would anyone do that?
  • You have a malicious actor on your trusted network.
    • If so, you have bigger problems.
  • You hit "Print" on a compromised network, such as a public library, while using CUPS.

Only the last one is potentially problematic for more people, and even then, the number of people using Linux is still very small. Some libraries don't allow printing or only printing via their computers.

It's good to know this flaw exists, but it doesn't seem like a particularly concerning attack vector.

[–] [email protected] 7 points 1 month ago (1 children)
  • You have a malicious actor on your trusted network.
  • If so, you have bigger problems.

This is more likely than you think. There's more computers than you realise on the average network. Many aren't updated and have vulnerabilities. If there's one malware on one machine on your network, that means a malicious actor is on your network.

Common exemples :

  • Home WiFi network with old unpached router, Android smartphone, network printer, security camera, thermostat, robot vacuum cleaner, smart lightbulb, smart TV, ...
  • Unsecure WiFi network at the cafe, train station, hotel, ... where you connect a laptops that is sometimes used for printing and which has CUPS
[–] [email protected] 1 points 1 month ago (1 children)

But again, most people aren't running Linux, and for people who are, they're likely more conscientious about connectivity and security patches.

I agree that most people aren't paying attention to every little thing, but the likelihood of someone invading your home network for a tiny payoff, especially when it requires the rare activity of printing something, is probably low-risk.

[–] [email protected] 2 points 1 month ago

But again, most people aren’t running Linux

Exactly. This is bad, for the 0.3% of the computing population that use Linux AND have CUPS installed AND actually print things.

Not exactly a prime target, compared to literally almost anything else. If I were going all-in on something after having gained access to someone's local network, I'm 100% in on any exploit that lets me use an infostealer trojan to steal your session cookies, not fiddling around and hoping you print something.

(Patch your shit anyways, but there's no need to freak out.)