CVE-2026-43037

What it is

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).

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.

Exploit odds

0.7% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-05-01 15:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-19 20:18 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.7% in the next 30 days (EPSS).
• Severity: 9.8 CRITICAL (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-05-01 15:16 UTC

Last modified

2026-10-19 20:18 UTC

Exploit probability

0.7% · EPSS, next 30 days

Weakness

CWE-787 · Out-of-bounds write

Record status

Modified

Affected

• Linux Kernel < 5.10.253
• Linux Kernel < 5.15.203
• Linux Kernel < 6.1.168
• Linux Kernel < 6.6.134
• Linux Kernel < 6.12.81
• Linux Kernel < 6.18.22
• Linux Kernel < 6.19.12
• Linux Kernel 7.0

Attack profile CVSS 3.1 · 9.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-43037.md and follow it. Check whether this project is affected by CVE-2026-43037. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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