CVE-2024-47176

A security issue was found in OpenPrinting CUPS. The function ppdCreatePPDFromIPP2 in the libppd library is responsible for generating a PostScript Printer Description (PPD) file based on attributes retrieved from an Internet Printing Protocol (IPP) response. Essentially, it takes printer information, usually obtained via IPP, and creates a corresponding PPD file that describes the printer’s capabilities (such as supported media sizes, resolutions, color modes, etc.). PPD files are used by printing systems like CUPS (Common Unix Printing System) to communicate with and configure printers. They provide a standardized format that allows different printers to work with the printing system in a consistent way. A security issue was discovered in OpenPrinting CUPS. The cups-browsed component is responsible for discovering printers on a network and adding them to the system. In order to do so, the service uses two distinct protocols. For the first one, the service binds on all interfaces on UDP port 631 and accepts a custom packet from any untrusted source. This is exploitable from outside the LAN if the computer is exposed on the public internet. The service also listens for DNS-SD / mDNS advertisements trough AVAHI. In both cases, when a printer is discovered by either the UDP packet or mDNS, its IPP or IPPS url is automatically contacted by cups-browsed and a Get-Printer-Attributes request is sent to it which can leak potentially sensitive system information to an attacker via the User-Agent header.

Mitigation

See the security bulletin for a detailed mitigation procedure.