dbcve.org
FreeBSDOperating system

CVE-2023-6660

MEDIUM · 6.5 CVSS v3.1 Published 2023-12-13
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

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 · unedited
When a program running on an affected system appends data to a file via an NFS client mount, the bug can cause the NFS client to fail to copy in the data to be written but proceed as though the copy operation had succeeded. This means that the data to be written is instead replaced with whatever data had been in the packet buffer previously. Thus, an unprivileged user with access to an affected system may abuse the bug to trigger disclosure of sensitive information. In particular, the leak is limited to data previously stored in mbufs, which are used for network transmission and reception, and for certain types of inter-process communication. The bug can also be triggered unintentionally by system applications, in which case the data written by the application to an NFS mount may be corrupted. Corrupted data is written over the network to the NFS server, and thus also susceptible to being snooped by other hosts on the network. Note that the bug exists only in the NFS client; the version and implementation of the server has no effect on whether a given system is affected by the problem.

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 confidence

A flaw in the NFS client causes data append operations to fail the copy-in step while incorrectly proceeding as if successful. This causes the intended data to be replaced with residual mbuf (memory buffer) contents previously stored in packet buffers, leading to potential sensitive information disclosure or data corruption sent to the NFS server.

MitigationApply vendor-supplied kernel patches for the NFS client; until patched, avoid mounting untrusted NFS exports and restrict NFS access to trusted networks to reduce exposure.

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
Affected:= 13.2= 14.0

CVSS 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
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Check FreeBSD version
    Run `uname -a` or `freebsd-version -k` to identify the installed FreeBSD version
    Affected if The version is 13.2 or 14.0 (exact match to the affected versions)
  2. Verify NFS client kernel module is loaded
    Run `kldstat | grep nfs` or check if /boot/kernel/nfscl.ko exists
    Affected if The nfscl kernel module is loaded, indicating NFS client functionality is available
  3. Identify active NFS mounts
    Run `mount | grep -E 'nfs|tmpfs' | grep -v procfs` or `showmount -e localhost` to list mounted NFS exports
    Affected if There are active NFS mounts using the local NFS client (the vulnerability affects client-side append operations)
  4. Check for NFS client daemon usage
    Run `ps aux | grep -E 'nfsd|nfscl' | grep -v grep` to see if NFS client processes are running
    Affected if NFS client processes are active, indicating the client feature is in use

You are affected if you are running FreeBSD 13.2 or 14.0 and actively using the NFS client to mount remote shares, as the flaw only triggers during client-side data append operations.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply vendor-supplied kernel patches for the NFS client; until patched, avoid mounting untrusted NFS exports and restrict NFS access to trusted networks to reduce exposure.

Recommended fix High confidence

FreeBSD 13.2-STABLE or later for 13.x systems; FreeBSD 14.1-RELEASE or later for 14.x systems

  1. Identify the current FreeBSD version using 'uname -r' or 'freebsd-version'
  2. For FreeBSD 13.x systems: Upgrade to FreeBSD 13.2-STABLE or later (or apply the security patch from FreeBSD Security Advisory FreeBSD-SA-23:18)
  3. For FreeBSD 14.x systems: Upgrade to FreeBSD 14.1-RELEASE or later (or apply the security patch from FreeBSD Security Advisory FreeBSD-SA-23:18)
  4. After upgrading, reboot the system to load the new kernel
  5. Verify the fix by checking that the kernel version includes the fix: look for 'nfsclient' module or kernel changes related to the mbuf copy operation in the NFS client
  6. Restart any NFS client mounts and verify they function correctly
Caveat FreeBSD major version upgrades may require updating third-party software or configurations; review the FreeBSD release notes for any breaking changes between 14.0 and 14.1

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in FreeBSD Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,880
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-6660 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data