CVE-2025-11234 in Red Hat
Summary
by MITRE • 10/03/2025
A flaw was found in QEMU. If the QIOChannelWebsock object is freed while it is waiting to complete a handshake, a GSource is leaked. This can lead to the callback firing later on and triggering a use-after-free in the use of the channel. This can be abused by a malicious client with network access to the VNC WebSocket port to cause a denial of service during the WebSocket handshake prior to the VNC client authentication.
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Analysis
by VulDB Data Team • 03/25/2026
The vulnerability identified as CVE-2025-11234 resides within the QEMU virtualization platform, specifically affecting the QIOChannelWebsock object implementation. This flaw represents a classic memory management issue that occurs during the asynchronous WebSocket handshake process used for VNC remote access. The vulnerability manifests when the QIOChannelWebsock object undergoes premature deallocation while still in the midst of a WebSocket handshake operation, creating a scenario where the associated GSource event source remains registered in the main loop but references freed memory. This memory management inconsistency creates a dangerous condition where the event source callback may execute at a later time when the memory has been reallocated or corrupted, leading to unpredictable behavior and potential system instability.
The technical exploitation of this vulnerability requires a malicious client to establish a network connection to the VNC WebSocket port and initiate a handshake process without completing it properly. The flaw stems from improper cleanup procedures in the object destruction sequence, where the GSource registration is not properly removed from the main event loop before the QIOChannelWebsock object is freed. This creates a use-after-free condition that can be triggered when the event source callback executes against the now-invalid memory location. The vulnerability is particularly concerning because it occurs during the initial handshake phase, before any authentication mechanisms are engaged, making it accessible to any network client with access to the VNC WebSocket port. According to CWE classification, this vulnerability maps to CWE-415: Double Free and CWE-416: Use After Free, representing multiple memory safety violations that can be leveraged for denial of service attacks.
The operational impact of CVE-2025-11234 extends beyond simple service disruption, as it represents a potential vector for more sophisticated attacks within virtualized environments. When exploited, the vulnerability can cause the QEMU process to crash or become unresponsive, effectively denying service to legitimate VNC clients attempting to establish connections. This denial of service can be particularly damaging in cloud computing environments or virtual desktop infrastructures where QEMU serves as the underlying hypervisor component for multiple virtual machines. The vulnerability's accessibility through network connections makes it particularly dangerous in multi-tenant environments where malicious actors could target specific VNC ports to disrupt services. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004: Endpoint Denial of Service and T1566.002: Phishing via Service, as it can be used to disrupt legitimate services and potentially serve as a stepping stone for further exploitation.
Mitigation strategies for CVE-2025-11234 should focus on immediate patching of affected QEMU versions and implementation of network-level controls to restrict access to VNC WebSocket ports. Organizations should ensure that VNC services are properly secured with strong authentication mechanisms and that network segmentation prevents unauthorized access to these ports. The fix typically involves ensuring proper cleanup of GSource registrations during object destruction and implementing additional safety checks to prevent premature deallocation during active handshake operations. System administrators should also consider implementing monitoring solutions to detect unusual patterns in VNC service behavior that might indicate exploitation attempts. Additionally, network access controls should be implemented to limit access to VNC WebSocket ports to trusted IP ranges only, reducing the attack surface for potential exploitation. Regular security assessments of virtualization environments are recommended to identify and remediate similar memory safety vulnerabilities that could provide similar attack vectors for denial of service or privilege escalation attacks.