CVE-2026-43037: In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_er

Q: How do I fix CVE-2026-43037?

linux kernel: upgrade to 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12. Exact commands for each OS are on this page.

Q: Is CVE-2026-43037 being exploited?

CVE-2026-43037 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-43037 affect?

CVE-2026-43037 affects linux kernel. Severity is critical (CVSS 9.8). In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADE

CVE-2026-43037 is a critical-severity flaw (CVSS 9.8) affecting linux kernel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset

Why this priority

Critical severity
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 47%)
CISA exploited list	No
Weakness	CWE-787, CWE-121, CWE-843
Published	2026-05-01
Last modified	2026-10-19

Publisher (CNA): kernel.org · Vendor: linux

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-01 15:16 UTCPublished CVE record published
2026-10-19 20:18 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 2.6.22 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 · 7.0 rc1

Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

Fedora 46 · fzssh · FIXED · 1.4.0-2.fc46 · FEDORA-2026-8004fcd067 · source

sudo dnf upgrade --advisory=FEDORA-2026-8004fcd067

Ubuntu 24.04 · linux · FIXED · 6.8.0-134.134

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.8.0-134.134" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 22.04 · linux · FIXED · 5.15.0-185.195

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.15.0-185.195" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 25.10 · linux · FIXED · 6.17.0-40.40

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.17.0-40.40" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 20.04 · linux · FIXED · 5.4.0-233.253

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.4.0-233.253" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 20.04 · linux-hwe-5.15 · FIXED · 5.15.0-185.195~20.04.1

sudo apt update && sudo apt install --only-upgrade linux-hwe-5.15 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux-hwe-5.15)" ge "5.15.0-185.195~20.04.1" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · linux · FIXED · 6.1.170-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.1.170-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · linux · FIXED · 6.12.85-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.12.85-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · kernel · FIXED · kernel-6.12.0-211.22.1.el10_2

sudo dnf upgrade --advisory=RHSA-2026:25191 rpm -q kernel

RHEL 10.0 Extended Update Support · kernel · FIXED · kernel-6.12.0-55.77.1.el10_0

sudo dnf upgrade --advisory=RHSA-2026:24343 rpm -q kernel

RHEL 6 Extended Lifecycle Support - EXTENSION · kernel · FIXED · kernel-2.6.32-754.61.1.el6

sudo dnf upgrade --advisory=RHSA-2026:27719 rpm -q kernel

RHEL 7 Extended Lifecycle Support · kernel-rt · FIXED · kernel-rt-3.10.0-1160.155.1.rt56.1307.el7

sudo dnf upgrade --advisory=RHSA-2026:41236 rpm -q kernel-rt

RHEL 7 Extended Lifecycle Support · kernel · FIXED · kernel-3.10.0-1160.153.1.el7

sudo dnf upgrade --advisory=RHSA-2026:27729 rpm -q kernel

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-1746 · source

sudo dnf update --advisory=ALAS2023-2026-1746

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:25217] Important: kernel security update 2026-06-11

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-43037?

linux kernel: upgrade to 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12. Exact commands for each OS are on this page.

Is CVE-2026-43037 being exploited?

CVE-2026-43037 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-43037 affect?

CVE-2026-43037 affects linux kernel. Severity is critical (CVSS 9.8). In the Linux kernel, the following vulnerability has been resolved: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() Oskar Kjos reported the following problem. ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6

How urgent is CVE-2026-43037?

Priority 60/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities

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References

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