CVE-2015-5239 in QEMU
Summary
by MITRE
Integer overflow in the VNC display driver in QEMU before 2.1.0 allows attachers to cause a denial of service (process crash) via a CLIENT_CUT_TEXT message, which triggers an infinite loop.
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Analysis
by VulDB Data Team • 10/01/2024
The vulnerability identified as CVE-2015-5239 represents a critical integer overflow flaw within the VNC display driver component of QEMU virtualization software. This issue affects QEMU versions prior to 2.1.0 and stems from inadequate input validation in the handling of CLIENT_CUT_TEXT messages. The vulnerability operates at the intersection of software security and virtualization integrity, where malicious actors can exploit this flaw to disrupt system operations. The VNC display driver serves as a crucial interface for remote desktop access within virtual machine environments, making this vulnerability particularly concerning for virtualization administrators and security professionals. The flaw manifests when the system processes certain client communication messages, specifically those related to clipboard text transfers, which can trigger unexpected behavior in the underlying memory management routines.
The technical implementation of this vulnerability involves an integer overflow condition that occurs during the processing of CLIENT_CUT_TEXT messages within the VNC protocol implementation. When an attacker sends a specially crafted message with malformed length parameters, the system's integer arithmetic operations exceed their maximum representable values, causing the signed integer to wrap around to negative values. This overflow condition directly leads to an infinite loop within the processing routine, as the system attempts to iterate using invalid loop parameters that exceed normal operational bounds. The vulnerability demonstrates characteristics consistent with CWE-190, which specifically addresses integer overflow conditions that can result in unexpected program behavior and system instability. The flaw operates through a classic buffer management error where the system fails to properly validate the size parameter before attempting to allocate memory or initiate processing loops.
The operational impact of CVE-2015-5239 extends beyond simple denial of service, representing a potential vector for more sophisticated attacks within virtualized environments. When the infinite loop is triggered, the affected QEMU process consumes excessive CPU resources and becomes unresponsive, effectively rendering the virtual machine inaccessible to legitimate users and administrators. This condition creates a denial of service scenario that can be exploited by unauthorized users to disrupt critical virtualized services, particularly in cloud computing environments where multiple virtual machines share underlying physical resources. The vulnerability is particularly dangerous in multi-tenant environments where one compromised virtual machine could potentially affect the performance and availability of other virtual machines running on the same host. From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.004, which involves network denial of service attacks targeting virtualization platforms.
Mitigation strategies for CVE-2015-5239 require immediate patching of affected QEMU installations to version 2.1.0 or later, where the integer overflow has been addressed through proper input validation and bounds checking. System administrators should implement network segmentation controls to limit access to VNC interfaces and reduce the attack surface available to potential exploiters. Additional protective measures include implementing monitoring solutions that can detect unusual CPU consumption patterns or process behavior that may indicate exploitation attempts. The fix implemented in QEMU 2.1.0 typically involves enhanced input validation routines that properly check integer parameters before processing and implementing appropriate overflow detection mechanisms. Organizations should also consider implementing network access controls that restrict VNC communication to trusted networks and employ authentication mechanisms to ensure only authorized users can establish VNC connections to virtual machines. Regular security assessments of virtualization environments are essential to identify and remediate similar vulnerabilities before they can be exploited in production systems.