CVE-2015-8504 in QEMU
Summary
by MITRE
Qemu, when built with VNC display driver support, allows remote attackers to cause a denial of service (arithmetic exception and application crash) via crafted SetPixelFormat messages from a client.
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Analysis
by VulDB Data Team • 08/29/2020
The vulnerability identified as CVE-2015-8504 affects QEMU virtualization software when configured with VNC display driver support, creating a critical security flaw that enables remote attackers to execute denial of service attacks. This vulnerability specifically targets the VNC protocol implementation within QEMU's display subsystem, where improperly handled SetPixelFormat messages can trigger arithmetic exceptions leading to application crashes. The flaw exists in the way QEMU processes VNC client communications, particularly when handling display format negotiations between the virtual machine and remote VNC clients.
The technical exploitation of this vulnerability occurs through crafted SetPixelFormat messages that contain malformed data or extreme values that cause integer arithmetic operations to overflow or underflow within QEMU's VNC implementation. When a remote attacker sends such malicious messages to a QEMU instance running with VNC support, the application fails to properly validate input parameters and subsequently processes these invalid values in arithmetic operations that result in exceptions. This leads to the application crashing and terminating the virtual machine display service, effectively causing a denial of service condition that disrupts normal operations for legitimate users who depend on the virtualized environment.
The operational impact of CVE-2015-8504 extends beyond simple service disruption as it can be exploited by attackers to systematically disable virtualization services across multiple systems. Organizations running QEMU-based virtualization platforms with VNC enabled are particularly vulnerable, as attackers can remotely target these systems without requiring authentication or elevated privileges. The vulnerability affects environments where QEMU serves as a hypervisor or where virtual machines are exposed to untrusted networks, making it a significant concern for cloud providers, data centers, and enterprise virtualization deployments. The crash condition can be repeated multiple times, potentially leading to sustained denial of service conditions that impact availability and reliability of virtualized infrastructure.
Mitigation strategies for this vulnerability include immediate application of security patches provided by QEMU maintainers and the broader open source community, which typically involve input validation improvements and proper arithmetic overflow handling within the VNC protocol implementation. System administrators should also consider disabling VNC support in QEMU configurations when it is not strictly required, implementing network segmentation to limit exposure of VNC services to trusted networks only, and monitoring for suspicious VNC client connections. Additionally, organizations should ensure their virtualization environments are properly configured with appropriate access controls and network firewalls to limit potential attack vectors. This vulnerability aligns with CWE-191, which describes integer underflow (wrap under) in software systems, and represents a typical example of how improper input validation in network protocols can lead to denial of service conditions that compromise system availability and can be exploited as part of broader attack campaigns targeting virtualization infrastructure.