CVE-2025-11234 is a use-after-free vulnerability identified in QEMU, specifically within the QIOChannelWebsock object that handles WebSocket connections for VNC services. The vulnerability arises when this object is freed while it is still waiting to complete the WebSocket handshake. This premature freeing leads to a GSource being leaked, which in turn causes a callback to be invoked later on a now-invalid memory reference, resulting in a use-after-free condition. This flaw can be exploited by a remote attacker with network access to the VNC WebSocket port to trigger a denial of service (DoS) by crashing the QEMU process during the handshake phase, before any VNC client authentication occurs. The vulnerability does not require any privileges or user interaction, making it remotely exploitable over the network. The CVSS v3.1 score is 7.5 (high severity), reflecting the ease of exploitation and the impact on availability, while confidentiality and integrity remain unaffected. The affected product is Red Hat Enterprise Linux 10 running QEMU version 2.6.0. No public exploits have been reported yet, but the vulnerability poses a significant risk to systems exposing the VNC WebSocket interface. The root cause is improper memory management in the asynchronous WebSocket handshake process, leading to a use-after-free scenario that can be weaponized for denial of service attacks.

For European organizations, this vulnerability primarily threatens the availability of virtualized environments running Red Hat Enterprise Linux 10 with QEMU VNC WebSocket services exposed. A successful exploitation can cause QEMU instances to crash, leading to service outages and potential disruption of critical workloads hosted on virtual machines. This is particularly impactful for sectors relying heavily on virtualization for cloud services, hosting, or internal infrastructure, such as finance, telecommunications, and government agencies. Since the attack can be launched remotely without authentication, any exposed VNC WebSocket ports represent a direct attack surface. Although confidentiality and integrity are not compromised, the denial of service could lead to operational downtime, loss of productivity, and potential cascading effects on dependent services. Organizations with strict uptime requirements or those operating critical infrastructure could face significant operational and reputational damage if exploited.

Organizations should prioritize updating QEMU to a patched version that addresses CVE-2025-11234 as soon as it becomes available from Red Hat or their respective Linux distributors. In the interim, network-level mitigations should be applied, including restricting access to the VNC WebSocket port via firewalls or network segmentation to trusted hosts only. Disabling the VNC WebSocket interface if not required can eliminate the attack vector. Monitoring network traffic for unusual connection attempts to the VNC WebSocket port can help detect potential exploitation attempts. Additionally, implementing intrusion detection systems (IDS) with signatures for anomalous WebSocket handshake behavior may provide early warning. Regularly auditing exposed services and minimizing the attack surface by disabling unnecessary features in QEMU and related virtualization components will reduce risk. Finally, organizations should prepare incident response plans for potential denial of service events affecting virtualization infrastructure.