CVE-2023-3255 is a vulnerability identified in the QEMU built-in VNC server component of Red Hat Enterprise Linux 8. The flaw is triggered during the processing of ClientCutText messages, which are used to transfer clipboard data from a VNC client to the server. Specifically, the vulnerability lies in the 'inflate_buffer' function that decompresses zlib-compressed clipboard data. Due to an incorrect exit condition in the loop handling this decompression, the function may enter an infinite loop when processing specially crafted attacker-controlled input. This infinite loop results in a denial of service (DoS) by causing the QEMU process to hang, potentially impacting the availability of virtual machines hosted on the affected system. Exploitation requires the attacker to be an authenticated VNC client with clipboard access, which limits the attack surface to authorized users or systems. The vulnerability does not affect confidentiality or integrity, as it does not allow code execution or data leakage. The CVSS v3.1 score is 6.5 (medium severity) with vector AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating network attack vector, low attack complexity, required privileges, no user interaction, unchanged scope, no confidentiality or integrity impact, but high impact on availability. No public exploits or active exploitation have been reported. The vulnerability was published on September 13, 2023, and affects Red Hat Enterprise Linux 8 systems running QEMU with the built-in VNC server enabled and clipboard sharing configured.

The primary impact of CVE-2023-3255 is a denial of service condition that can disrupt the availability of virtual machines running on Red Hat Enterprise Linux 8 hosts using QEMU with the built-in VNC server. For European organizations, this could lead to temporary outages of critical virtualized infrastructure, affecting business continuity, especially in sectors relying heavily on virtualization such as finance, telecommunications, government, and cloud service providers. Since the attack requires authenticated access to the VNC server clipboard feature, the risk is higher in environments where VNC access is granted to multiple users or where authentication controls are weak. The lack of confidentiality or integrity impact reduces the risk of data breaches or system compromise, but the availability disruption could still cause operational and reputational damage. Organizations with high availability requirements or those operating critical infrastructure should consider this vulnerability significant enough to warrant prompt remediation. The absence of known exploits in the wild reduces immediate risk but does not eliminate the potential for future exploitation.

To mitigate CVE-2023-3255, European organizations should take the following specific actions: 1) Apply the latest security patches and updates provided by Red Hat for Red Hat Enterprise Linux 8 and QEMU as soon as they become available to fix the infinite loop condition. 2) Restrict VNC server access to trusted and authenticated users only, enforcing strong authentication mechanisms such as multi-factor authentication to reduce the attack surface. 3) Disable clipboard sharing over VNC if it is not required, as this feature is the attack vector for the vulnerability. 4) Monitor VNC server logs and network traffic for unusual clipboard activity or repeated connection attempts that could indicate exploitation attempts. 5) Implement network segmentation and firewall rules to limit VNC access to only necessary systems and users. 6) Consider alternative remote management tools or VNC implementations that do not exhibit this vulnerability if patching is delayed. 7) Conduct regular vulnerability assessments and penetration tests focusing on virtualization infrastructure to identify and remediate similar issues proactively.