CVE-2019-6778 in QEMU
Summary
by MITRE
In QEMU 3.0.0, tcp_emu in slirp/tcp_subr.c has a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 10/26/2024
The vulnerability identified as CVE-2019-6778 represents a critical heap-based buffer overflow flaw within QEMU version 3.0.0, specifically affecting the tcp_emu function located in the slirp/tcp_subr.c source file. This issue arises within the network stack implementation of QEMU's slirp networking subsystem, which provides user-mode network connectivity for virtual machines. The vulnerability stems from insufficient input validation and bounds checking when processing TCP emulation operations, creating a scenario where malicious network traffic can trigger memory corruption. The flaw is particularly concerning because it exists within the core networking functionality that virtual machines rely upon for external communication, making it a prime target for exploitation in virtual machine escape scenarios.
The technical implementation of this vulnerability involves the tcp_emu function's handling of TCP packet data within the slirp network emulation layer. When processing incoming TCP connections or data streams, the function fails to properly validate the length of incoming data buffers before copying them into fixed-size heap-allocated memory regions. This allows an attacker controlling network traffic to send specially crafted TCP packets that exceed the allocated buffer boundaries, resulting in memory corruption that can overwrite adjacent heap data structures. The heap-based nature of the overflow means that the corruption affects the program's dynamic memory management system, potentially leading to arbitrary code execution or denial of service conditions. This type of vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a classic example of insufficient bounds checking in memory management operations.
The operational impact of CVE-2019-6778 extends beyond simple denial of service scenarios, as it creates potential pathways for privilege escalation and virtual machine escape attacks. When exploited successfully, this vulnerability could allow an attacker positioned on the same network segment as a virtual machine to gain unauthorized access to the host system or other virtual machines running on the same hypervisor. The implications are particularly severe in cloud computing environments where multiple tenants share the same physical infrastructure, as a compromised virtual machine could potentially be used to attack other guests or the underlying host system. Network security professionals should consider this vulnerability in the context of ATT&CK framework's T1055 technique for privilege escalation and T1071 for application layer protocol usage, as the exploit could leverage legitimate network traffic patterns to avoid detection. The vulnerability affects QEMU versions up to and including 3.0.0, making it particularly relevant for organizations maintaining older virtualization environments that have not received the necessary security patches.
Mitigation strategies for CVE-2019-6778 should prioritize immediate patching of QEMU installations to versions that contain the fix for this heap-based buffer overflow. Organizations should implement network segmentation and access controls to limit exposure of virtual machines to untrusted networks, particularly in environments where network traffic cannot be fully trusted. Network monitoring solutions should be configured to detect anomalous TCP packet patterns that might indicate exploitation attempts, focusing on unusual data payload sizes or malformed TCP headers. Additionally, virtual machine administrators should consider implementing network access control lists and firewall rules to restrict network communication between virtual machines and external networks. The vulnerability demonstrates the importance of maintaining up-to-date virtualization software and implementing comprehensive security monitoring for virtual environments, as highlighted in industry best practices for hypervisor security and secure virtual machine configuration. Regular vulnerability assessments and penetration testing should include evaluation of virtualization components to identify similar memory corruption vulnerabilities that could provide similar attack vectors.