Comment on Critical Unauthenticated RCE Flaws in CUPS Printing Systems
mox@lemmy.sdf.org 2 months ago
Exploitation involves sending a malicious UDP packet to port 631 on the target, directing it to an attacker-controlled IPP server.
Okay, so at least until this is patched, it would be a good idea to shut down any process that’s listening on port 631, and avoid interaction with untrusted or potentially compromised print servers.
Either of these commands will list any such processes:
$ sudo lsof -i :631
$ sudo fuser -v 631/tcp 631/udp
Toes@ani.social 2 months ago
What are your thoughts on the alternative path the article talks about “…zeroconf, mDNS, or DNS-SD advertisements”?
mox@lemmy.sdf.org 2 months ago
That refers to the fact that printer advertisements can contain lies: Although you might see a familiar printer name appear on a network, it might secretly point to the address of a malicious device.
So my first advice stands: Avoid interaction with untrusted or potentially compromised print servers.
To be clear, when I say “interaction”, I don’t just mean printing to them. I mean any interaction at all. Even just browsing a network for printers could potentially mean your system contacts the devices at the advertised addresses, and receives data from them. This Qualys report doesn’t make clear whether this kind of interaction is safe, so I have to assume for now that it is not.
lemmyvore@feddit.nl 2 months ago
How do you avoid interaction if it’s being done automatically by your machine when you open up a print dialog, and if malicious servers can use the same names as legit printers?
mox@lemmy.sdf.org 2 months ago
I suppose I would avoid connecting to untrusted networks, or avoid opening print dialogs while on them, or uninstall CUPS until a fix is available.