CVE-2025-9903 is an out-of-bounds write vulnerability classified under CWE-787, affecting Canon Inc.'s Generic Plus printer drivers, including PCL6, UFR II, LIPS4, LIPSLX, PS, UFRII LT, CARPS2, and Generic FAX drivers, specifically versions 3.30 and earlier. The vulnerability occurs during the print processing phase, where improper handling of input data leads to writing outside the intended memory bounds. This can corrupt adjacent memory, potentially altering program behavior or causing crashes. The CVSS 3.1 base score is 5.9 (medium severity), with the vector indicating network attack vector (AV:N), high attack complexity (AC:H), no privileges required (PR:N), user interaction required (UI:R), unchanged scope (S:U), no confidentiality impact (C:N), high integrity impact (I:H), and low availability impact (A:L). The high attack complexity and requirement for user interaction reduce the likelihood of exploitation, and no known exploits have been reported. The vulnerability affects a broad range of Canon printer drivers used in various environments, including office and enterprise print servers. The absence of patches at publication time necessitates interim mitigations. The flaw could be exploited by sending specially crafted print jobs to vulnerable printers, potentially causing memory corruption that may lead to denial of service or integrity violations in print processing. This could disrupt printing services or corrupt print output, impacting business operations.

For European organizations, this vulnerability poses risks primarily to the integrity and availability of printing services. Disruption of print infrastructure can affect document workflows, especially in sectors reliant on physical documentation such as government, healthcare, and manufacturing. While confidentiality is not directly impacted, integrity compromises could lead to altered or corrupted printouts, potentially affecting compliance and operational accuracy. The medium CVSS score reflects moderate risk, but the requirement for user interaction and high attack complexity limit widespread exploitation. However, targeted attacks against critical infrastructure or high-value organizations could leverage this vulnerability to cause denial of service or manipulate printed information. Organizations with extensive Canon printer deployments or centralized print servers are more vulnerable. The lack of known exploits reduces immediate threat but does not eliminate future risk, especially as attackers develop proof-of-concept exploits. The impact is heightened in environments where printer drivers are not regularly updated or where network segmentation is weak, allowing easier access to vulnerable devices.

1. Restrict network access to Canon printers and print servers by implementing strict firewall rules and network segmentation to limit exposure to untrusted networks. 2. Enforce user awareness and training to avoid opening or processing suspicious print jobs, as exploitation requires user interaction. 3. Monitor print server and network logs for unusual print job patterns or errors indicative of exploitation attempts. 4. Disable unnecessary printer driver features or services that process external input if feasible. 5. Maintain an inventory of all Canon printer drivers and versions in use to identify vulnerable instances. 6. Engage with Canon for timely release of patches and apply updates promptly once available. 7. Consider deploying endpoint protection solutions that can detect anomalous behavior related to print processing. 8. Implement least privilege principles on print servers to limit potential damage from exploitation. 9. Test print infrastructure resilience regularly to ensure rapid recovery from potential denial of service incidents. 10. Use network intrusion detection systems with signatures for print protocol anomalies to detect exploitation attempts early.