CUPS facing the public internet sounds a bit crazy. Why would you print when not physicly near the printer?
this post was submitted on 29 Sep 2024
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I think this would likely be most troublesome on some of the OG internet users that got a whole freaking /8, /10, or /12 or something like AT&T or universities. Up until very recently, and possibly even to the present, these organizations had such large IPv4 space, that there was no need to do NAT, and each device had a publicly addressable IP.
https://en.wikipedia.org/wiki/List_of_assigned_/8_IPv4_address_blocks
Everything would still be behind a firewall though
everything should be behind a firewall
The questionable commit:
{
// Add the first line of localized text...
cupsFilePrintf(fp, "*%s.%s %s/", lang->language, ppd_option, ppd_choice);
while (*text && *text != '\n')
{
// Escape ":" and "<"...
if (*text == ':' || *text == '<')
cupsFilePrintf(fp, "<%02X>", *text);
else
cupsFilePutChar(fp, *text);
text ++;
}
cupsFilePuts(fp, ": \"\"\n");
}
Can someone explain to me how this allows arbitrary code execution? As far as I can see, all it does iterate through a string and markup some special characters.
Edit: Okay, after reading the blog post, and this fantastic bug report, it sounds like to print to a CUPS server, you send it a message on port 631 using an IPP (some print protocol) server. CUPS then requests attributes of the IPP server, one of which being the print filter command to run ("Foomatic-rip") to use to convert a PS or PDF into native print code. By requesting attributes, an exploit involving string escaping through the use of unexpected spaces or quotes can override the Foomatic print command. Arbitrary text can be supplanted, which will then be executed by the CUPS server.
From what I understand, this allows arbitrary command execution. So, an attacker can specify a string of text that something on the affected system will just plop into a command line and execute.
Take a look at the exploit code
Can I just disable CUPS?
Any self-respecting distro pushed an update to fix this days ago, so just updating (and restarting cups) will do. But if you don't print anyway, you might as well disable it.
Man, this is such a silly and unfortunate exploit. Damn! I hope it gets patched quick.