CVE-2019-5609 in FreeBSD
Summary
by MITRE
In FreeBSD 12.0-STABLE before r350619, 12.0-RELEASE before 12.0-RELEASE-p9, 11.3-STABLE before r350619, 11.3-RELEASE before 11.3-RELEASE-p2, and 11.2-RELEASE before 11.2-RELEASE-p13, the bhyve e1000 device emulation used a guest-provided value to determine the size of the on-stack buffer without validation when TCP segmentation offload is requested for a transmitted packet. A misbehaving bhyve guest could overwrite memory in the bhyve process on the host.
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Analysis
by VulDB Data Team • 08/10/2020
The vulnerability described in CVE-2019-5609 represents a critical memory corruption issue within the FreeBSD bhyve hypervisor's e1000 network device emulation. This flaw exists in multiple FreeBSD versions including 11.2-RELEASE through 11.3-RELEASE and 12.0-RELEASE, specifically affecting systems running versions prior to the mentioned patch releases. The vulnerability manifests when the bhyve hypervisor processes network packets with TCP segmentation offload enabled, creating a scenario where guest operating systems can manipulate memory layout through crafted network traffic.
The technical implementation of this vulnerability stems from inadequate input validation within the e1000 device emulation layer. When a guest system requests TCP segmentation offload for transmitted packets, the bhyve hypervisor utilizes a value provided by the guest to determine the size of an on-stack buffer. This guest-provided value is never properly validated or sanitized before being used to allocate memory resources. The absence of bounds checking or size validation creates a classic buffer overflow condition that allows malicious guests to overwrite adjacent memory regions within the hypervisor process space.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides a potential pathway for privilege escalation and system compromise. An attacker controlling a bhyve guest virtual machine could leverage this vulnerability to execute arbitrary code within the host system context, effectively breaking the isolation guarantees that hypervisors are designed to maintain. This represents a severe security regression that undermines the fundamental security model of virtualization environments. The vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1059 for execution through hypervisor manipulation.
Mitigation strategies for CVE-2019-5609 require immediate patching of affected FreeBSD systems to the recommended release versions that contain the necessary fixes. Organizations running bhyve hypervisors should prioritize updating their systems to versions 11.3-RELEASE-p2, 11.2-RELEASE-p13, or 12.0-RELEASE-p9 and later. Additional defensive measures include implementing network segmentation to limit guest access to potentially malicious network traffic, monitoring for unusual memory allocation patterns in hypervisor processes, and restricting guest virtual machine capabilities where possible. The vulnerability highlights the importance of proper input validation in hypervisor components and demonstrates how guest-controlled data can be exploited to compromise host security boundaries.