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Linux KernelOperating system · Linux

CVE-2026-43384

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-08
Fix available
A fix is available. Upgrade to 6.12.78 / 6.18.19 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: net/tcp-ao: Fix MAC comparison to be constant-time To prevent timing attacks, MACs need to be compared in constant time. Use the appropriate helper function for this.

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 · moderate confidence

The Linux kernel's TCP Authentication Option (TCP-AO) implementation uses a non-constant-time comparison for Message Authentication Codes (MACs). This allows timing attacks where an attacker can deduce MAC values by measuring comparison execution times. The fix involves replacing the standard comparison with a constant-time comparison helper function.

MitigationApply the Linux kernel update containing the constant-time MAC comparison fix for TCP-AO. If TCP-AO is in use, prioritize this update given the critical CVSS score and network-exploitable timing attack vector.

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:>= 6.7, < 6.12.78>= 6.13, < 6.18.19>= 6.19, < 6.19.9= 7.0

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
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 the installed kernel version
    Run `uname -r` to get the kernel version, or read `/proc/version`
    Affected if The kernel version falls within any of these ranges: >= 6.7 and < 6.12.78; >= 6.13 and < 6.18.19; >= 6.19 and < 6.19.9; or exactly version 7.0. If the version is unknown, compare your installed version to these ranges.
  2. Verify TCP-AO kernel support is present
    Check the kernel configuration file (usually in `/boot/config-$(uname -r)` or `/proc/config.gz`) for `CONFIG_TCP_AO=y` or `CONFIG_TCP_AO=m`, or check if the tcp_ao module is loaded with `lsmod | grep tcp_ao`
    Affected if TCP-AO support is compiled into the kernel or loaded as a module (the vulnerability only applies if TCP-AO functionality is available)
  3. Determine if TCP-AO is actively in use
    Inspect active network connections for TCP-AO usage by checking `/proc/net/tcp_ao` (if it exists) or using `ss --ao` to display connections with TCP-AO authentication, or query the netlink interface for AO-enabled sockets
    Affected if There are active TCP connections using TCP-AO authentication (the vulnerability is only exploitable when TCP-AO is actually being used to protect connections)

You are affected only if your kernel version is in the affected ranges AND TCP-AO is both available and actively protecting at least one TCP connection.

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 6.12.78 / 6.18.19 / 6.19.9 or later
Fixed in 6.12.786.18.196.19.9
Vendor patch git.kernel.org →
Interim mitigation

Apply the Linux kernel update containing the constant-time MAC comparison fix for TCP-AO. If TCP-AO is in use, prioritize this update given the critical CVSS score and network-exploitable timing attack vector.

Recommended fix High confidence

Upgrade to kernel 6.12.78+, 6.18.19+, 6.19.9+, or 7.1+ depending on your current branch

  1. Check current kernel version with: uname -r
  2. For kernels 6.7 to 6.12.x: Upgrade to kernel 6.12.78 or later
  3. For kernels 6.13 to 6.18.x: Upgrade to kernel 6.18.19 or later
  4. For kernels 6.19.x: Upgrade to kernel 6.19.9 or later
  5. For kernel 7.0.x: Upgrade to kernel 7.1 or later
  6. After upgrading, reboot the system to load the new kernel
  7. Verify the fix is applied by checking the kernel version: uname -r
Caveat Kernel upgrades typically require system reboot and may require driver/module recompilation for out-of-tree modules

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
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,920
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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-2026-43384 in production — separate from our analysis above.

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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