Linux kernel IPv6 ICMP control-buffer type confusion leading to out-of-bounds write
CVE-2026-43038 is a Linux kernel networking flaw in IPv6 ICMP error handling, specifically in ip6_err_gen_icmpv6_unreach(). The vulnerable path clones an skb representing an outer IPv4 ICMP error packet into skb2 without clearing skb2->cb[]. The original control buffer contains IPv4 inet_skb_parm state, but the cloned packet is later passed to icmp6_send(), which interprets the same cb area as IPv6 inet6_skb_parm via IP6CB(skb2). Because fields overlap in memory, the cipso offset in inet_skb_parm.opt can be reinterpreted as the dsthao field in inet6_skb_parm. A forged ICMPv4 error carrying a CIPSO IP option can therefore make dsthao non-zero and influence subsequent IPv6 option parsing. In icmp6_send(), mip6_addr_swap() calls ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO), causing scanning of an inner attacker-controlled IPv6 packet from an attacker-influenced offset. The reported issue is that this can yield a fake Home Address Option TLV without ensuring sufficient remaining packet length for the full struct ipv6_destopt_hao, creating the possibility of a 16-byte swap extending past packet data and into adjacent skb memory. The fix clears skb2->cb[] in ip6_err_gen_icmpv6_unreach() before IPv6 processing.
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