CVE-2026-43038

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < c438ba010171b70bad22fc18b1d5bdc3627476e8affected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < 0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7affected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < a4437faf135da293d16fcc4cc607316742bd0ebbaffected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < 3d5127d998de617b130aae96b138dba22ac6a8a7affected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < e41953e7d118e2702bcb217879c173d9d1d3cd4eaffected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < a2edbb6393972a02114b6003953a5cef3104fadaaffected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < 1ceeebd5bd6d855b17a5df625109bfe29129d7cfaffected
LinuxLinuxca15a078bd907df5fc1c009477869c5cbde3b753 < 86ab3e55673a7a49a841838776f1ab18d23a67b5affected
LinuxLinux3.13affected
LinuxLinux0 < 3.13unaffected
LinuxLinux5.10.253 <= 5.10.*unaffected
LinuxLinux5.15.203 <= 5.15.*unaffected
LinuxLinux6.1.168 <= 6.1.*unaffected
LinuxLinux6.6.134 <= 6.6.*unaffected
LinuxLinux6.12.81 <= 6.12.*unaffected
LinuxLinux6.18.22 <= 6.18.*unaffected
LinuxLinux6.19.12 <= 6.19.*unaffected
LinuxLinux7.0 <= *unaffected

Weaknesses

ADP Enrichment

kernel: ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

Additional References

References