This software security report provides an analysis of possible security concerns for the Common UNIX Printing System ("CUPS") Version 1.1.
This software security report is organized into the following sections:
Local access risks are those that can be exploited only with a local user account. This section does not address issues related to dissemination of the root password or other security issues associated with the UNIX operating system.
There is one known security vulnerability with local access:
We recommend that any password-protected accounts used for remote printing have limited access priviledges so that the possible damages can be minimized.
The device URI is "sanitized" (the username and password are removed) when sent to an IPP client so that a remote user cannot exploit this vulnerability.
Remote access risks are those that can be exploited without a local user account and/or from a remote system. This section does not address issues related to network or firewall security.
Like all Internet services, the CUPS server is vulnerable to denial of service attacks, including:
Starting with CUPS 1.1.18, the MaxClientsPerHost provides limited protection against DoS attacks, however it is not effective against large-scale distributed attacks.
MaxClientsPerHost
There is no easy way of protecting against this in the CUPS software. If the attack is coming from outside the local network it might be possible to filter such an attack, however once the connection request has been received by the server it must at least accept the connection to find out who is connecting.
It might be possible to disable browsing if this condition is detected by the CUPS software, however if there are large numbers of printers available on the network such an algorithm might think that an attack was occurring when instead a valid update was being received.
The current code is structured to read and write the IPP request data on-the-fly, so there is no easy way to protect against this for large attribute values.
There are limited facilities for protecting against large print jobs (the MaxRequestSize attribute), however this will not protect printers from malicious users and print files that generate hundreds or thousands of pages. In general, we recommend restricting printer access to known hosts or networks, and adding user-level access control as needed for expensive printers.
MaxRequestSize
The current CUPS server supports Basic, Digest, and local certificate authentication:
/etc/cups/certs
The default CUPS configuration disables remote administration. We do not recommend that remote administration be enabled for all hosts. However, if you have a trusted network or subnet, access can be restricted accordingly. Also, we highly recommend using Digest authentication when possible. Unfortunately, most web browsers do not support Digest authentication at this time.