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).

No CVSS v4.0

Attack Vector Local

Attack Complexity High

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
Linux Linux unaffected
Version Status Constraints
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < ea9f65b27c8404e164848ebff1443310fd187629
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < d6621f60192fe10c047a4487be42a6f4c150707f
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < a0c4ce9900a108eaf55d0f3b399cb55999647d39
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < 1063515ce15ff31065c4e7f8265f4c2fd3c54876
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < 4a622658f384b03560834cbe8ffcfe69a278f7c8
c4d3efafcc933fd2ffd169d7dc4f980393a13796 affected < 2edfa31769a4add828a7e604b21cb82aaaa05925
Linux Linux affected
Version Status Constraints
2.6.22 affected —
0 unaffected < 2.6.22
5.10.253 unaffected ≤ 5.10.*
5.15.203 unaffected ≤ 5.15.*
6.1.168 unaffected ≤ 6.1.*
6.6.134 unaffected ≤ 6.6.*
6.12.81 unaffected ≤ 6.12.*
6.18.22 unaffected ≤ 6.18.*
6.19.12 unaffected ≤ 6.19.*
7.0 unaffected ≤ *

No data.

No data.

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Advisories
Source ID Title
Debian DSA Debian DSA DSA-6243-1 linux security update
Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876 cve-icon cve-icon
https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5 cve-icon cve-icon
https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925 cve-icon cve-icon
https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8 cve-icon cve-icon
https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3 cve-icon cve-icon
https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39 cve-icon cve-icon
https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f cve-icon cve-icon
https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629 cve-icon cve-icon
https://lore.kernel.org/linux-cve-announce/2026050102-CVE-2026-43037-0346@gregkh/T cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-43037 cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-43037 cve-icon
History

Sat, 02 May 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Important

Fri, 01 May 2026 23:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-120

Fri, 01 May 2026 14:45:00 +0000

Type Values Removed Values Added
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).
Title ip6_tunnel: clear skb2->cb[] in ip4ip6_err()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-05-01T14:15:35.314Z

Reserved: 2026-05-01T14:12:55.978Z

Link: CVE-2026-43037

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-05-01T15:16:48.383

Modified: 2026-05-01T15:24:14.893

Link: CVE-2026-43037

cve-icon Redhat

Severity : Important

Publid Date: 2026-05-01T00:00:00Z

Links: CVE-2026-43037 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-05-01T23:15:29Z

Weaknesses