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Linux KernelOperating system · Linux

CVE-2026-43011

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-01
Fix available
A fix is available. Upgrade to 5.10.253 / 5.15.203 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/x25: Fix potential double free of skb When alloc_skb fails in x25_queue_rx_frame it calls kfree_skb(skb) at line 48 and returns 1 (error). This error propagates back through the call chain: x25_queue_rx_frame returns 1 | v x25_state3_machine receives the return value 1 and takes the else branch at line 278, setting queued=0 and returning 0 | v x25_process_rx_frame returns queued=0 | v x25_backlog_rcv at line 452 sees queued=0 and calls kfree_skb(skb) again This would free the same skb twice. Looking at x25_backlog_rcv: net/x25/x25_in.c:x25_backlog_rcv() { ... queued = x25_process_rx_frame(sk, skb); ... if (!queued) kfree_skb(skb); }

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's X.25 protocol implementation (net/x25). When alloc_skb fails in x25_queue_rx_frame, it frees the skb and returns an error, but the caller's error handling sets queued=0, causing x25_backlog_rcv to free the same skb again, resulting in memory corruption.

MitigationApply the kernel patch that prevents the double-free by correcting the return value handling in x25_state3_machine or preventing the redundant kfree_skb call in x25_backlog_rcv when x25_queue_rx_frame has already failed.

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:>= 2.6.12.1, < 5.10.253>= 5.11, < 5.15.203>= 5.16, < 6.1.168>= 6.2, < 6.6.134>= 6.7, < 6.12.81>= 6.13, < 6.18.22>= 6.19, < 6.19.12= 2.6.12= 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 your kernel version
    Run 'uname -r' or 'cat /proc/version' to get the exact kernel version
    Affected if The version falls within the affected ranges: >= 2.6.12.1 and < 5.10.253; >= 5.11 and < 5.15.203; >= 5.16 and < 6.1.168; >= 6.2 and < 6.6.134; >= 6.7 and < 6.12.81; >= 6.13 and < 6.18.22; >= 6.19 and < 6.19.12; or equals 2.6.12 or 7.0
  2. Verify if X.25 kernel module is loaded
    Run 'lsmod | grep x25' or check /proc/modules for 'x25' entry
    Affected if The x25 module is loaded (vulnerability only applies when X.25 protocol support is active)
  3. Check if X.25 network interface exists
    Run 'ip link show' or 'cat /proc/net/x25' to list active X.25 interfaces
    Affected if An X.25 interface is configured and active (the double-free occurs when processing frames on an X.25 interface)

You are affected if your kernel version is in the affected ranges AND the X.25 module is loaded with an active X.25 interface, because the double-free only triggers in the x25_queue_rx_frame -> x25_backlog_rcv call path when processing received X.25 frames.

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 5.10.253 / 5.15.203 / 6.1.168 or later
Fixed in 5.10.2535.15.2036.1.168
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel patch that prevents the double-free by correcting the return value handling in x25_state3_machine or preventing the redundant kfree_skb call in x25_backlog_rcv when x25_queue_rx_frame has already failed.

Recommended fix High confidence

Upgrade to kernel version 5.10.253, 5.15.203, 6.1.168, 6.6.134, or later stable release depending on your distribution's kernel series

  1. Identify the currently running Linux kernel version using `uname -r`
  2. Based on the current kernel version, upgrade to one of the following fixed releases: 5.10.253, 5.15.203, 6.1.168, or 6.6.134 (or any later stable release)
  3. For Debian/Ubuntu: Run `sudo apt-get update && sudo apt-get dist-upgrade` to get the latest kernel
  4. For RHEL/CentOS: Run `sudo yum update kernel`
  5. For Fedora: Run `sudo dnf update kernel`
  6. After upgrading the kernel package, reboot the system to load the fixed kernel: `sudo reboot`
  7. Verify the new kernel version after reboot using `uname -r`
Caveat Kernel upgrades may require system restart and could introduce compatibility changes with third-party modules; ensure custom drivers are compatible with the new kernel version

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
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
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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-2026-43011 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
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