CVE-2026-43037

Critical

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).

Package Linux Kernel
Published 2026-05-01
Last modified 2026-05-04
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

9.8

out of 10
Critical
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness type

CWE-787

CVE-2026-43037 is a Out-of-bounds Write vulnerability

What is Out-of-bounds Write?

The product writes data past the end or before the beginning of the intended buffer. Learn more on MITRE CWE

Affected versions

Linux kernel versions 2.6.22 and later are affected. Fixed in 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12, 7.0 and their respective stable series.

Affected from
≥ 2.6.22
Fixed in
✓ 5.10.253 5.10.x ✓ 5.15.203 5.15.x ✓ 6.1.168 6.1.x ✓ 6.6.134 6.6.x ✓ 6.12.81 6.12.x ✓ 6.18.22 6.18.x ✓ 6.19.12 6.19.x ✓ 7.0

References

The following references provide additional information about CVE-2026-43037 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

8 patch commits total View all on NVD

Frequently asked questions

  • What is CVE-2026-43037?

    CVE-2026-43037 is a Critical severity Linux kernel vulnerability with a CVSS score of 9.8 out of 10 , classified as an Out-of-bounds Write flaw (CWE-787) . It affects Linux kernel versions from 2.6.22 onward and has been patched in 5.10.253, 5.15.203, 6.1.168 and others. CVE-2026-43037 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2026-43037?

    CVE-2026-43037 has a CVSS score of 9.8 out of 10, rated Critical severity (CVSS 3.1). The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H .

  • Is there a patch available for CVE-2026-43037?

    Yes — CVE-2026-43037 has been patched. Fixed versions include 5.10.253, 5.15.203, 6.1.168 and others. If you are running Linux kernel 2.6.22 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2026-43037 actively exploited?

    No — CVE-2026-43037 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

  • What is Out-of-bounds Write (CWE-787)?

    The product writes data past the end or before the beginning of the intended buffer. View CWE-787 on MITRE CWE →

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