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Linux KernelOperating system · Linux

CVE-2026-31609

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-24
Fix available
A fix is available. Upgrade to 6.18.24 / 6.19.14 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: smb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush() smbd_send_batch_flush() already calls smbd_free_send_io(), so we should not call it again after smbd_post_send() moved it to the batch list.

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 double-free vulnerability exists in the Linux kernel SMB client where smbd_free_send_io() is called both within smbd_send_batch_flush() and redundantly after smbd_post_send() when the I/O is moved to the batch list, causing use-after-free and potential privilege escalation.

MitigationApply the Linux kernel patch that removes the redundant smbd_free_send_io() call. Since this is a kernel-level fix, systems using the SMB client (particularly with RDMA/smbd) should be updated during a scheduled maintenance window.

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:< 6.18.24>= 6.19, < 6.19.14>= 7.0, < 7.0.1

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. Identify your kernel version
    Run `uname -r` or `cat /proc/version` to get the exact kernel version
    Affected if The version falls within < 6.18.24, >= 6.19 to < 6.19.14, or >= 7.0 to < 7.0.1
  2. Verify the SMB client kernel module is loaded
    Run `lsmod | grep -E 'smbd|smb' ` to check if SMB-related kernel modules are loaded
    Affected if The smbd or smb3 modules are loaded in memory
  3. Confirm smbd service is active
    Run `systemctl status smbd` or check for smbd processes via `ps aux | grep smbd`
  4. Check if RDMA is enabled for SMB
    Examine `/sys/class/infiniband/` directory contents and check SMB configuration files under `/etc/samba/` for 'rdma' settings
    Affected if RDMA support is configured or enabled in the SMB client setup

You are affected if your kernel version is in one of the vulnerable ranges AND the SMB client with smbd/RDMA support is actively in use.

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 6.18.24 / 6.19.14 / 7.0.1 or later
Fixed in 6.18.246.19.147.0.1
Vendor patch git.kernel.org →
Interim mitigation

Apply the Linux kernel patch that removes the redundant smbd_free_send_io() call. Since this is a kernel-level fix, systems using the SMB client (particularly with RDMA/smbd) should be updated during a scheduled maintenance window.

Recommended fix High confidence

6.18.24, 6.19.14, or 7.0.1

  1. Identify the currently running kernel version using 'uname -r'
  2. Check which distribution-specific kernel package is installed (e.g., for Debian/Ubuntu: 'dpkg -l | grep linux-image', for RHEL/CentOS: 'rpm -qa | grep kernel')
  3. Update the package repository metadata
  4. Install the fixed kernel version: For Debian/Ubuntu: 'apt-get install linux-image-<fixed-version>' or 'apt-get upgrade linux-image-generic'
  5. For RHEL/CentOS: 'yum install kernel-<fixed-version>' or 'dnf install kernel-<fixed-version>'
  6. For distributions using kpatch/mlivepatch, consider applying a live patch if available
  7. Reboot the system to load the fixed kernel using 'systemctl reboot' or 'shutdown -r now'
  8. After reboot, verify the running kernel is the fixed version with 'uname -r'
Caveat Kernel upgrades may require driver rebuilds or system configuration adjustments; ensure compatibility with installed modules and custom drivers before rebooting

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

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA3.0 h
14.0 hours of engineering $2,400
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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-2026-31609 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