CVE-2023-3494: bhyve privileged guest escape via fwctl

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-08-01 · updated 2026-06-17
Weakness: CWE-120

Description

The fwctl driver implements a state machine which is executed when a bhyve guest accesses certain x86 I/O ports. The interface lets the guest copy a string into a buffer resident in the bhyve process' memory. A bug in the state machine implementation can result in a buffer overflowing when copying this string. Malicious, privileged software running in a guest VM can exploit the buffer overflow to achieve code execution on the host in the bhyve userspace process, which typically runs as root, mitigated by the capabilities assigned through the Capsicum sandbox available to the bhyve process.

Affected products

FreeBSD: 13.1, 13.1-b1-p1, 13.1-b2-p2, 13.1-p1, 13.1-p2, 13.1-p3 (+8)

References

Get alerted when CVE-2023-3494 or the next vulnerability affects your stack