CVE-2015-1779 in QEMU
Summary
by MITRE
The VNC websocket frame decoder in QEMU allows remote attackers to cause a denial of service (memory and CPU consumption) via a large (1) websocket payload or (2) HTTP headers section.
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Analysis
by VulDB Data Team • 04/16/2022
The vulnerability identified as CVE-2015-1779 resides within the VNC websocket frame decoder implementation in QEMU virtualization software, representing a critical denial of service weakness that can be exploited remotely by malicious actors. This flaw specifically affects the handling of websocket frames within the QEMU virtual machine monitor, where insufficient validation and resource management leads to excessive memory and CPU consumption during payload processing. The vulnerability manifests when QEMU encounters websocket frames with either excessively large payload data or oversized HTTP headers sections, creating a scenario where legitimate system resources become consumed at an unsustainable rate. The VNC websocket functionality in QEMU serves as a remote access mechanism for virtual machine management, making this vulnerability particularly concerning for cloud environments and virtualization platforms that rely heavily on remote desktop protocols. Attackers can leverage this weakness to perform resource exhaustion attacks that effectively render virtual machines unavailable to legitimate users, disrupting service availability and potentially causing cascading failures in virtualized infrastructures.
The technical nature of this vulnerability stems from inadequate input validation within the websocket frame processing pipeline of QEMU's VNC implementation. When the system receives a websocket frame containing oversized payload data or HTTP headers, the decoder fails to properly enforce size limitations or implement appropriate resource allocation controls. This allows malicious payloads to trigger unbounded memory allocation and processing cycles, where the virtual machine monitor consumes increasing amounts of system resources without proper bounds checking. The vulnerability operates at the protocol level within the VNC implementation, specifically targeting the websocket frame decoding logic that handles incoming remote connections. The flaw represents a classic resource exhaustion attack vector where the attacker can manipulate the decoder to consume system resources proportional to the size of the malicious input, making it particularly effective against systems with limited memory or CPU capacity. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a fundamental weakness in software design that leads to denial of service conditions.
The operational impact of CVE-2015-1779 extends beyond simple service disruption to encompass broader system stability and availability concerns within virtualized environments. Organizations utilizing QEMU-based virtualization platforms face significant risk of cascading failures when this vulnerability is exploited, as resource exhaustion on one virtual machine can affect the entire host system and potentially impact other virtual machines running on the same infrastructure. The vulnerability is particularly dangerous in cloud computing environments where multiple tenants share the same physical hardware, as a single malicious user could potentially disrupt services for other users on the same host. Attackers can exploit this weakness with minimal technical expertise, requiring only the ability to establish a VNC connection to the target virtual machine and send specifically crafted websocket frames. The memory and CPU consumption patterns created by this vulnerability can be difficult to detect in real-time monitoring systems, as the resource usage may appear legitimate until it reaches critical thresholds. This makes the vulnerability particularly insidious as it can be used to maintain persistent denial of service conditions without triggering immediate security alerts.
Mitigation strategies for CVE-2015-1779 should focus on implementing robust input validation and resource limitation mechanisms within the QEMU VNC implementation. Organizations should prioritize applying the official QEMU patches released by the project maintainers, which typically include enhanced bounds checking and memory allocation controls for websocket frame processing. Network-level mitigations can include implementing rate limiting and connection throttling mechanisms to prevent rapid resource exhaustion attacks, while also deploying monitoring systems that can detect unusual memory and CPU consumption patterns. Security configurations should enforce strict limits on websocket payload sizes and HTTP header lengths, preventing malicious inputs from reaching the vulnerable decoder logic. System administrators should also consider implementing network segmentation and access controls to limit exposure of QEMU VNC services to trusted networks only, reducing the attack surface available to potential adversaries. Additionally, regular security audits and vulnerability assessments should be conducted to identify similar weaknesses in other components of the virtualization stack, as this vulnerability demonstrates the importance of proper resource management in protocol implementations. The ATT&CK framework categorizes this vulnerability under the resource exhaustion technique, where adversaries leverage software weaknesses to consume system resources and create denial of service conditions, making it essential for organizations to implement both defensive and detection capabilities to address such threats effectively.