CVE-2026-43037: Linux Kernel type confusion (CVSS 9.8)

Description

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 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE). To fix this we clear skb2->cb[], as suggested by Oskar Kjos. Also add minimal IPv4 header validation (version == 4, ihl >= 5).

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Linux Kernel≥ 2.6.22 < 5.10.253 · ≥ 5.11 < 5.15.203 · ≥ 5.16 < 6.1.168 · ≥ 6.13 < 6.18.22

Remediation

Fixed in

Linux Kernel≥ 5.10.253

Patch & vendor advisories

References

and 36 more references

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-43037 being actively exploited?

CVE-2026-43037 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.83%.

How severe is CVE-2026-43037?

CVE-2026-43037 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.83% probability of exploitation.

Which products are affected by CVE-2026-43037?

Affected products include Linux Kernel.

How do I fix CVE-2026-43037?

Upgrade affected software to a fixed version, for example Linux Kernel 5.10.253 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-43037 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation works Book a demo