Critical Unauthenticated RCE Flaws in CUPS Printing Systems | Qualys Security Blog
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A critical set of unauthenticated Remote Code Execution (RCE) vulnerabilities in CUPS, affecting all GNU/Linux systems and potentially others, was disclosed today. These vulnerabilities allow a remote…
  • mox
    2•1 hour 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 CUPS-related 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

    I don’t want to diminish the urgency of this vulnerability, but it is worth noting that “affecting all GNU/Linux systems” does not mean that every affected system is actually running the vulnerable code. Some installations don’t run print services.

    Also, I suspect that the author’s use of “GNU” in that warning is misleading. (Sadly, a certain unfortunate meme has led many people to think that all Linux systems are GNU systems.) I don’t see any reason to think musl builds of CUPS are immune, for example, so I don’t assume my Alpine systems are safe just because they are not GNU/Linux.

    • Toes♀
      OP
      1•36 minutes ago

      What are your thoughts on the alternative path the article talks about “…zeroconf, mDNS, or DNS-SD advertisements”?

      • mox
        1•7 minutes 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.