FreeBSDOperating system
CVE-2023-3494
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedThe 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceBuffer overflow vulnerability in the fwctl driver state machine of the bhyve hypervisor. When a guest VM accesses certain x86 I/O ports, the driver copies a guest-supplied string into a buffer without proper bounds checking, allowing a malicious privileged guest to overflow the buffer and achieve code execution in the bhyve process (typically running as root). The Capsicum sandbox provides some mitigation.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
FreeBSDOperating system
= 13.1= 13.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check FreeBSD versionRun 'freebsd-version' or 'uname -r' to determine the installed FreeBSD versionAffected if Version is 13.1 or 13.2 (both affected versions)
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Verify bhyve installationRun 'which bhyve' or check if bhyve binaries exist in /usr/sbin/bhyveAffected if bhyve is installed and available on the system
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Identify running bhyve processesRun 'ps aux | grep bhyve' or check for active VM processesAffected if bhyve VMs are currently running (exploitation requires a guest VM with access to the vulnerable x86 I/O ports)
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Check for privileged guest configurationsExamine VM configuration files for settings that grant guests elevated privileges or direct I/O port access (such as '-w' flag or similar privilege escalation options in bhyve command lines)Affected if Guest VMs are configured with privileged access that allows manipulation of x86 I/O ports
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Verify Capsicum sandbox statusReview bhyve process execution context - check if Capsicum sandbox is in use via process audit or by examining how bhyve was launchedAffected if Capsicum sandbox is NOT enabled (lack of sandboxing increases exploitability but does not affect whether the vulnerability exists)
You are affected if you are running FreeBSD 13.1 or 13.2 with bhyve and have active guest VMs that have privileged access to x86 I/O ports used by the fwctl driver.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply vendor patches for this vulnerability in bhyve/FreeBSD. If patches are unavailable, consider restricting VM privileges, using seccomp or additional sandboxing around bhyve processes, or upgrading to a patched FreeBSD version.
Fix this in FreeBSD
Scoped from the published advisory
- Consultation3.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,568.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-3494 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2023-3494 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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