CVE-2016-1889 in FreeBSD
Summary
by MITRE
Integer overflow in the bhyve hypervisor in FreeBSD 10.1, 10.2, 10.3, and 11.0 when configured with a large amount of guest memory, allows local users to gain privilege via a crafted device descriptor.
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Analysis
by VulDB Data Team • 06/20/2019
The vulnerability identified as CVE-2016-1889 represents a critical integer overflow flaw within the bhyve hypervisor component of FreeBSD operating systems version 10.1 through 10.3 and 11.0. This issue specifically manifests when the hypervisor is configured to handle substantial amounts of guest memory, creating a scenario where malicious local users can exploit the flaw to escalate their privileges. The vulnerability resides in the hypervisor's handling of device descriptors, which are essential components for managing virtualized hardware resources within the virtual machine environment. The integer overflow occurs during the processing of these device descriptors, where insufficient bounds checking allows for arithmetic overflow conditions that can be manipulated by an attacker.
The technical exploitation of this vulnerability leverages the hypervisor's memory management routines to create a condition where integer values exceed their maximum representable range, leading to unexpected behavior in memory allocation and handling. When a large amount of guest memory is configured, the bhyve hypervisor's device descriptor processing becomes particularly susceptible to this overflow condition. The flaw is classified as a CWE-190 Integer Overflow or Wraparound, which is a well-documented vulnerability pattern where arithmetic operations produce results that exceed the maximum value that can be represented by the data type. This type of vulnerability is particularly dangerous in hypervisor contexts as it can provide attackers with direct access to the underlying system resources and potentially full system compromise.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally compromises the security isolation that hypervisors are designed to maintain between virtual machines and the host system. Local users who can access the hypervisor interface or have the ability to configure device descriptors can manipulate the integer overflow to gain elevated privileges, potentially allowing them to execute arbitrary code with kernel-level access. This represents a severe breach of the hypervisor's security model, as the attack vector does not require network access or external exploitation methods. The vulnerability affects systems where bhyve is actively used for virtualization, particularly in environments where multiple users have local access to the system or where device descriptor configuration is exposed to untrusted parties. The attack can be executed through carefully crafted device descriptors that trigger the overflow condition during memory allocation processes, potentially leading to complete system compromise.
Mitigation strategies for CVE-2016-1889 focus primarily on patching the FreeBSD hypervisor implementation to address the integer overflow condition in device descriptor processing. System administrators should immediately apply the relevant security patches released by FreeBSD to correct the memory handling routines that permit the overflow condition. Additionally, implementing strict access controls on hypervisor configuration interfaces can help prevent unauthorized users from manipulating device descriptors. The mitigation approach aligns with ATT&CK technique T1068, which involves exploiting legitimate credentials and system access to escalate privileges, though in this case the escalation occurs through hypervisor-level manipulation rather than credential theft. Organizations should also consider reducing the amount of guest memory configured in bhyve environments where possible, as this can limit the attack surface by reducing the likelihood of triggering the overflow condition. Network segmentation and monitoring of hypervisor activities can provide additional layers of defense by detecting anomalous behavior patterns that may indicate exploitation attempts. The vulnerability demonstrates the critical importance of input validation and bounds checking in hypervisor code, as even seemingly benign operations like device descriptor processing can become attack vectors when proper safeguards are absent.