Printer bug sends researchers into uproar, affects major Linux distros

OpenPrinting's libcupsfilters, the library providing CUPS filter functionality for printer data-format conversion, fails to sanitize IPP attributes returned from IPP servers in its cfGetPrinterAttributes5 function (CWE-20, CVSS 8.6). The flaw is triggered when a system running CUPS contacts an attacker-controlled or untrusted IPP server and uses the returned attributes, for example to generate a PPD file, allowing attacker-controlled data to flow into the rest of the CUPS system. On its own this yields high-integrity attacker data injection (per the CVSS vector, no direct confidentiality or availability loss), but it is one of several CUPS flaws disclosed together in late September 2024 that, when chained under certain conditions, can result in remote code execution on Linux and Unix systems. Any system running libcupsfilters is affected; CUPS and its filter libraries ship by default with most major Linux distributions, and public internet scans around disclosure found roughly 75,000 hosts exposing the IPP service (TCP 631) directly to the internet. Proof-of-concept details are public (an EvilSocket writeup and the OpenPrinting GitHub advisory GHSA-w63j-6g73-wmg5), the flaw is not yet in CISA KEV, and EPSS assigns a 77.6% probability of exploitation within 30 days, though no confirmed in-the-wild exploitation appears in the provided data.

Do: Upgrade libcupsfilters to the patched release identified in the OpenPrinting advisory GHSA-w63j-6g73-wmg5 (fixed in libcupsfilters 2.1.0), applying your distribution's updated cups-filters/CUPS packages; also install the companion CUPS component fixes released the same week, since this flaw is typically chained with other CUPS bugs (notably in cups-browsed) for remote code execution. Until patched, restrict or disable exposure of the IPP service (TCP 631) to untrusted networks and avoid creating or refreshing printer queues from untrusted or mDNS-advertised IPP servers.

CVE-2024-47175 is an improper input validation flaw (CWE-20) in OpenPrinting's libppd: the ppdCreatePPDFromIPP2 function fails to sanitize IPP attributes when writing them into a generated PPD buffer. When this unsanitized, attacker-controlled input flows through the CUPS print pipeline — for example via the cups-browsed entry point abused in CVE-2024-47176, in combination with functions such as cfGetPrinterAttributes5 — it can ultimately be executed by Foomatic print filters, giving remote code execution. Affected systems are Linux/Unix hosts running the CUPS printing stack with vulnerable libppd components, which includes widely used distributions such as Debian and, per press coverage, most other major Linux distros. Exploitation status: public proofs of concept and researcher write-ups exist, the flaw carries a high EPSS score (63.6% probability of exploitation within 30 days, 99th percentile) and warnings about abuse including DDoS, but it is not yet in CISA's KEV catalog, so no confirmed widespread in-the-wild exploitation is documented in the available data.

Do: Install your distribution's security updates — upgrade libppd to the patched release (2.1b1 or later, per the OpenPrinting advisory GHSA-7xfx-47qg-grp6) and apply the matching cups/cups-filters fixes. As interim mitigation, disable or stop cups-browsed if not needed and block or restrict inbound UDP 631 (and IPP/port 631 generally) from untrusted networks, particularly on internet-facing hosts. Check whether CUPS is running and reachable on your systems and whether configured printers rely on Foomatic filters, which the RCE chain requires.

CVE-2024-47176 is a flaw in cups-browsed, the network printer auto-discovery component of the OpenPrinting CUPS printing stack shipped with most major Linux and Unix distributions, which binds to UDP port 631 on all interfaces (INADDR_ANY) and therefore accepts and trusts unauthenticated packets from any source. A remote attacker can send a crafted browse/IPP packet that makes cups-browsed issue a Get-Printer-Attributes IPP request to an attacker-controlled URL. On its own this flaw is rated Medium (5.3), but chained with companion flaws in libcupsfilters (CVE-2024-47076), libppd (CVE-2024-47175), and cups-filters (CVE-2024-47177) it enables unauthenticated arbitrary command execution when a user prints to the attacker's malicious printer; the exposure has also been noted as abusable for DDoS amplification. Any Linux/Unix system running cups-browsed with UDP/631 reachable from an untrusted network is affected. No confirmed widespread in-the-wild exploitation has been reported and the flaw is not yet in CISA's KEV, but public proofs of concept exist and EPSS assigns a ~51% probability of exploitation within 30 days (99th percentile).

Do: Update cups-browsed and the companion cups-filters/libcupsfilters/libppd packages to the patched releases published by OpenPrinting and your distribution alongside the September 2024 advisories (see GHSA-rj88-6mr5-rcw8). If patched packages are not yet available, stop or disable the cups-browsed service, or firewall inbound UDP port 631 from untrusted networks and ensure it binds only to localhost where network printer discovery is not needed. Audit whether cups-browsed is running and whether UDP/631 is reachable from the internet, and treat any network-reachable CUPS host as a candidate for the full RCE chain.

Rejected reason: ** REJECT ** DO NOT USE THIS CANDIDATE NUMBER. ConsultIDs: CVE-2024-47076, CVE-2024-47175, CVE-2024-47176. Reason: This candidate is a duplicate of CVE-2024-47076, CVE-2024-47175, and CVE-2024-47176. Notes: All CVE users should reference CVE-2024-47076, CVE-2024-47175, and/or CVE-2024-47176 instead of this candidate. This CVE was issued to a vulnerability that is dependent on CVE-2024-47076, CVE-2024-47175, and CVE-2024-47176. According to rule 4.2.15 of the CVE CNA rules, \"CNAs MUST NOT assign a different CVE ID to a Vulnerability that is fully interdependent with another Vulnerability. The Vulnerabilities are effectively the same single Vulnerability and MUST use one CVE ID.