CVE-2026-43037

Summary

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).

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < ea9f65b27c8404e164848ebff1443310fd187629affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < d6621f60192fe10c047a4487be42a6f4c150707faffected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < a0c4ce9900a108eaf55d0f3b399cb55999647d39affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < 1063515ce15ff31065c4e7f8265f4c2fd3c54876affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < 4a622658f384b03560834cbe8ffcfe69a278f7c8affected
LinuxLinuxc4d3efafcc933fd2ffd169d7dc4f980393a13796 < 2edfa31769a4add828a7e604b21cb82aaaa05925affected
LinuxLinux2.6.22affected
LinuxLinux0 < 2.6.22unaffected
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: ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

Additional References

References