CVE-2026-43038: Linux Kernel type confusion (CVSS 9.8)

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach() Sashiko AI-review observed: In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2 and passed to icmp6_send(), it uses IP6CB(skb2). IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm at offset 18. If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called and uses ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO). This would scan the inner, attacker-controlled IPv6 packet starting at that offset, potentially returning a fake TLV without checking if the remaining packet length can hold the full 18-byte struct ipv6_destopt_hao. Could mip6_addr_swap() then perform a 16-byte swap that extends past the end of the packet data into skb_shared_info? Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and ip6ip6_err() to prevent this? This patch implements the first suggestion. I am not sure if ip6ip6_err() needs to be changed. A separate patch would be better anyway.

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≥ 5.11 < 5.15.203 · ≥ 5.16 < 6.1.168 · ≥ 6.13 < 6.18.22 · ≥ 6.19 < 6.19.12

Remediation

Fixed in

Linux Kernel≥ 5.15.203

Patch & vendor advisories

References

and 22 more references

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-43038 being actively exploited?

CVE-2026-43038 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.26%.

How severe is CVE-2026-43038?

CVE-2026-43038 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.26% probability of exploitation.

Which products are affected by CVE-2026-43038?

Affected products include Linux Kernel.

How do I fix CVE-2026-43038?

Upgrade affected software to a fixed version, for example Linux Kernel 5.15.203 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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