CVE-2026-43038
Published: 01 May 2026
Summary
CVE-2026-43038 is a critical-severity Type Confusion (CWE-843) vulnerability in Linux Linux Kernel. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 16.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
This vulnerability is AI-related — categorised as Other Platforms; in the Protocol-Specific Risks risk domain.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-7 (Boundary Protection).
Deeper analysis
CVE-2026-43038 is a vulnerability in the Linux kernel's IPv6 ICMP error handling, specifically within the ip6_err_gen_icmpv6_unreach() function. The issue arises when processing an outer IPv4 ICMP error packet containing a CIPSO IP option; the skb is cloned into skb2 without clearing its cb[] array. This causes IP6CB(skb2) to misinterpret the IPv4 inet_skb_parm as an inet6_skb_parm, where the cipso offset overlaps with dsthao at offset 18. Consequently, icmp6_send() invokes mip6_addr_swap(), which uses ipv6_find_tlv() to scan the inner attacker-controlled IPv6 packet starting at a non-zero offset, potentially identifying a fake TLV without validating the remaining packet length for the full 18-byte struct ipv6_destopt_hao, leading to a possible 16-byte swap extending into skb_shared_info.
Remote attackers with network access can exploit this by sending forged IPv4 ICMP error packets with a crafted CIPSO option, requiring no privileges or user interaction (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). Successful exploitation could enable kernel memory corruption through the out-of-bounds memory operation in mip6_addr_swap(), compromising confidentiality, integrity, and availability with critical severity.
Kernel patches address the vulnerability by clearing skb2->cb[] in ip6_err_gen_icmpv6_unreach(), as implemented in stable commits such as 0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7, 1ceeebd5bd6d855b17a5df625109bfe29129d7cf, 3d5127d998de617b130aae96b138dba22ac6a8a7, 86ab3e55673a7a49a841838776f1ab18d23a67b5, and a2edbb6393972a02114b6003953a5cef3104fada. A separate patch for ip6ip6_err() may be warranted but is not included here.
The flaw was observed by Sashiko AI-review, highlighting AI-assisted kernel auditing. No real-world exploitation is reported.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-26637
Vulnerability details
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…
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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.
- CWE(s)
AI Security AnalysisAI
- AI Category
- Other Platforms
- Risk Domain
- Protocol-Specific Risks
- OWASP Top 10 for LLMs 2025
- None mapped
- Classification Reason
- Matched keywords: ai
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes a remotely exploitable kernel memory corruption vulnerability in IPv6 ICMP handling, directly enabling exploitation of public-facing systems (T1190) and privilege escalation via kernel compromise (T1068).
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely identification, reporting, and patching of the Linux kernel flaw in ip6_err_gen_icmpv6_unreach() directly resolves the skb cb[] misinterpretation leading to out-of-bounds memory access.
Kernel memory protection mechanisms such as KASLR, SMEP, and SMAP mitigate the impact of out-of-bounds swaps in mip6_addr_swap() by randomizing addresses and restricting unauthorized memory access.
Boundary protection devices like firewalls can filter or rate-limit forged IPv4 ICMP error packets with crafted CIPSO options, preventing them from reaching the vulnerable IPv6 error handling path.