dbcve.org
Linux KernelOperating system · Linux

CVE-2026-31718

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-01
Fix available
A fix is available. Upgrade to 6.7 / 6.12.84 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

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
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger When a durable file handle survives session disconnect (TCP close without SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the handle for later reconnection. However, it did not clean up the byte-range locks on fp->lock_list. Later, when the durable scavenger thread times out and calls __ksmbd_close_fd(NULL, fp), the lock cleanup loop did: spin_lock(&fp->conn->llist_lock); This caused a slab use-after-free because fp->conn was NULL and the original connection object had already been freed by ksmbd_tcp_disconnect(). The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were left dangling on the freed conn->lock_list while fp->conn was nulled out. To fix this issue properly, we need to handle the lifetime of smb_lock->clist across three paths: - Safely skip clist deletion when list is empty and fp->conn is NULL. - Remove the lock from the old connection's lock_list in session_fd_check() - Re-add the lock to the new connection's lock_list in ksmbd_reopen_durable_fd().

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 use-after-free vulnerability in the Linux kernel's ksmbd SMB server occurs when a durable file handle survives session disconnect. The session_fd_check() function nullifies fp->conn to preserve the handle but fails to clean up byte-range locks on fp->lock_list. When the durable scavenger later calls __ksmbd_close_fd(NULL, fp), it attempts to access fp->conn->llist_lock on an already-freed connection, causing a slab use-after-free.

MitigationApply the kernel patch that properly handles smb_lock->clist lifetime by cleaning up locks from the old connection's lock_list in session_fd_check() and re-adding them in ksmbd_reopen_durable_fd(), while safely skipping deletion when fp->conn is NULL.

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
Linux KernelOperating system
Affected:>= 6.6.32, < 6.7>= 6.9, < 6.12.84>= 6.13, < 6.18.25>= 6.19, < 7.0.2= 7.1

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
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 checks

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

  1. Check kernel version against affected ranges
    Run 'uname -r' to get the kernel version, then compare it to: >= 6.6.32 and < 6.7; >= 6.9 and < 6.12.84; >= 6.13 and < 6.18.25; >= 6.19 and < 7.0.2; = 7.1
    Affected if The kernel version falls within any of these ranges and ksmbd is in use
  2. Verify ksmbd module is loaded
    Run 'lsmod | grep ksmbd' or check /sys/module/ksmbd/ to see if the ksmbd kernel module is loaded
    Affected if The ksmbd module is loaded on an affected kernel version
  3. Check if ksmbd daemon is running
    Run 'ps aux | grep ksmbd' or check for ksmbd service process (user-space SMB server)
    Affected if The ksmbd daemon process is running on an affected kernel version
  4. Confirm SMB server is configured and active
    Check /etc/ksmbd/ksmbd.conf or running 'smbstatus' if Samba tools are available to see active SMB connections
    Affected if SMB shares are being served by ksmbd, allowing session disconnect scenarios with durable file handles

You are affected if your kernel version is in the affected ranges AND ksmbd (either as kernel module or user-space daemon) is actively serving SMB connections that can trigger session disconnect with durable handle scenarios.

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
Upgrade available Upgrade to 6.7 / 6.12.84 / 6.18.25 or later
Fixed in 6.76.12.846.18.25
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel patch that properly handles smb_lock->clist lifetime by cleaning up locks from the old connection's lock_list in session_fd_check() and re-adding them in ksmbd_reopen_durable_fd(), while safely skipping deletion when fp->conn is NULL.

Recommended fix High confidence

Upgrade to Linux Kernel 6.12.84, 6.18.25, or 7.0.2 or later (whichever is available for your distribution)

  1. Identify the currently running Linux kernel version using `uname -r` or `hostnamectl`
  2. Download or obtain the upgraded kernel package for your distribution that matches or exceeds version 6.12.84, 6.18.25, or 7.0.2
  3. For production systems, test the kernel upgrade in a staging environment first to ensure compatibility with hardware and workloads
  4. Apply the kernel upgrade via your distribution's package manager (e.g., `apt-get dist-upgrade`, `yum update`, or `dnf upgrade`)
  5. Reboot the system to load the new kernel using `sudo reboot`
  6. After reboot, verify the running kernel version with `uname -r` and confirm it includes the fix (version >= 6.12.84, >= 6.18.25, or >= 7.0.2)
  7. If running ksmbd (SMB kernel server), verify the service operates normally post-upgrade
Caveat Kernel upgrades may require matching kernel modules; ensure all proprietary drivers (NVIDIA, etc.) are compatible with the target kernel version before upgrading

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

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,888.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-31718 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-31718 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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