CVE-2021-3942 is a critical vulnerability identified in certain HP Inc. Print products and Digital Sending products. The flaw arises from improper handling of Link-Local Multicast Name Resolution (LLMNR) requests, which can lead to a buffer overflow condition. Specifically, this vulnerability is categorized under CWE-119, indicating a classic buffer overflow issue where the software does not properly validate or limit the size of input data before copying it into a fixed-length buffer. Exploiting this vulnerability allows an unauthenticated remote attacker to execute arbitrary code on the affected device without requiring any user interaction. The attack vector is network-based (AV:N), meaning the attacker can exploit it remotely over the network. The vulnerability has a CVSS v3.1 base score of 9.8, reflecting its critical severity due to high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The scope is unchanged (S:U), meaning the exploit affects only the vulnerable component itself. No privileges or user interaction are required (PR:N/UI:N), which significantly lowers the barrier to exploitation. Although no known exploits have been reported in the wild as of the publication date, the potential for remote code execution makes this a high-risk vulnerability, especially in enterprise environments where HP printing and digital sending devices are widely deployed. The affected versions are detailed in HP’s security bulletin, and organizations using these products should consult that resource for precise patching guidance. The vulnerability’s root cause is linked to the handling of LLMNR, a network protocol used for name resolution on local networks, which if manipulated by an attacker, can trigger the buffer overflow and subsequent code execution.

For European organizations, the impact of CVE-2021-3942 could be severe. HP Print and Digital Sending products are commonly used in corporate, governmental, and educational institutions across Europe for document management and communication workflows. Successful exploitation could allow attackers to gain full control over these devices, leading to unauthorized access to sensitive documents, interception or manipulation of data being printed or sent digitally, and potential lateral movement within the network. This could result in data breaches, disruption of business operations, and compromise of confidentiality and integrity of critical information. Given the devices’ network connectivity and integration into IT infrastructure, attackers could leverage compromised printers as footholds to escalate privileges or pivot to other systems. The lack of required authentication and user interaction increases the risk of automated or widespread exploitation attempts. Additionally, disruption or denial of service against these devices could impact operational continuity, especially in environments relying heavily on digital document workflows. The vulnerability’s exploitation could also undermine trust in organizational security postures and lead to regulatory compliance issues under GDPR if personal or sensitive data is exposed.

To mitigate CVE-2021-3942 effectively, European organizations should take the following specific actions beyond generic patching advice: 1) Immediately consult HP’s official security bulletin to identify affected product models and firmware versions and apply the provided patches or firmware updates without delay. 2) Disable LLMNR protocol on network segments where HP Print and Digital Sending devices operate if patching is not immediately feasible, as this reduces the attack surface by preventing exploitation via LLMNR requests. 3) Segment printer and digital sending devices on dedicated VLANs with strict access controls to limit exposure to untrusted networks and reduce the risk of lateral movement. 4) Implement network monitoring and intrusion detection systems tuned to detect anomalous LLMNR traffic or unusual activity patterns associated with exploitation attempts. 5) Enforce strict network access policies, including limiting which hosts can communicate with printing devices, and use network-level authentication where supported. 6) Conduct regular security audits and vulnerability assessments on printing infrastructure to ensure timely identification and remediation of similar issues. 7) Educate IT and security teams about the risks associated with network protocols like LLMNR and the importance of securing peripheral devices. These targeted measures, combined with patching, will significantly reduce the risk posed by this vulnerability.